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kbpepperell
This noise is killing me!
kbpepperell

I'm going to try to post this in a few boards because people are telling me it's not HVAC, and my cousin is in HVAC and he thinks the sound is water pressure related, but my husband and I are literally losing sleep over this so we need to find an answer.

To start, we live in Minneapolis, MN, and we bought the house in May 2015. The house has a forced-air central heating system. It was cool weather when we bought it, so I think we were still using the furnace on occasion. If I'm remembering correctly, we turned the a/c on for the first time in June. The a/c compressor has an on/off switch that was turned off when we bought the house. So we turned that on, and switched the thermostat to a/c. At some point shortly thereafter, we heard the noise for the first time. Sometimes we go weeks without hearing it. Sometimes it happens every hour (like today). It woke us up three times last night.

I hope this is allowed (and I hope the link works) -- I posted a short video of one of the high whistling sound. This is a publicly shared video on Google Drive: https://drive.google.com/file/d/0BzCXINv9QlCjTzJBejRGRlFkVlU/view?usp=sharing

Here are the facts we feel pretty sure of:

  • It happens during the warmer months, and maybe even on warmer days
  • It happens during the night and day but doesn't seem to be related to anything triggering it (happens when we're all asleep but also happens when we're all awake and using water, etc.)
  • It happens most often when the a/c system is on (thermostat set to cool), but has also happened when the system was off, but never happens with the a/c is running
  • Kicking the a/c on to blow air is the only thing that stops the noise
  • Sometimes it's a low moaning noise, sometimes it's a high whistling noise (like in the video), sometimes it's both
  • We've tried shutting off the main water valve but that doesn't stop it
  • The vibration can be felt when touching the furnace/ductwork in the basement
  • Most events last at least several minutes
  • We're on city water (not well) and we've had the water heater replaced in the time we've been here and it has not changed anything
  • We have a central humidifier but the valve is off in the summer

We had an HVAC technician come out twice. The first time he said it was a dirty filter (we have a crazy 20x20x4 filter). We replaced the filter but it made no difference. The second time he came out (in July), we were lucky enough to have him experience the noise first hand. It was happening frequently then and now we're back to July and it's going crazy again. The following is my husband's account of the conversation on the second visit:

So, the technician was unable to find the source of the noise. He said it was unrelated to the HVAC system, because the blower in the furnace wasn't running at the time the noise occurred. It's definitely something vibrating the trunk/ducting around the furnace, but he wasn't able to say what the cause was. There are some copper pipes running next to the furnace so he speculated that could be the cause, but he said it was just a guess.

I know this is a long post but I appreciate any help that can be offered. We don't know where to go from here. And thanks to those who have taken the time to read this whole post...hopefully someone has heard of a something similar before and has ideas for a solution! :) Kristine

ed21
Re: This noise is killing me!
ed21

I was going to suggest it may be a plumbing issue with a toilet valve or pressure reducer, but after listening to your video I don't think so. When it happens can you kill the power to the whole house at the breaker box? If that stops the sound you can turn on each circuit one at a time to see if it comes back. Or just start at the breaker for the a/c and see if it stops.
Not being an a/c tech, a/c works by using high pressure gas. Some sort of malfunction in a valve might make a sound like that. You didn't mention a heat pump which are just more complicated air conditioners, but I doubt you have one in Minneapolis. Contacting another HVAC company or even the manufacturer of the unit might get you an answer or an idea about what's happening. Turning off the power may have no effect if it's gas within the unit.

kbpepperell
Re: This noise is killing me!
kbpepperell

My plan right now is to try every (reasonable) suggestion I get. So, this goes to the top of the list! Thanks for taking the time to reply.

A. Spruce
Re: This noise is killing me!
A. Spruce

Security settings on my computer won't allow the link to the noise, so unfortunately, I don't have much to offer.

ed21 wrote:

Turning off the power may have no effect if it's gas within the unit.

No, but it would single out the HVAC as opposed to something else in the house.

While I'm not a tech, a heat pump basically works by reversing the flow of gas in the system, run it on AC and the cooling coils outside exhaust the heat in the freon gas. Run the heat (heat pump) and the fins inside the air handler/house cools the freon gas. This works, even in cold climates, because freon boils at something like -200 degrees, so while the temps outside might be cold, they're not -200 cold, there is still heat transfer to the system.

Reading the description of the noise, it does seem most likely that it is the HVAC unit in some manner, however, it could be a form of water hammer, typically something that happens when faucets are turned off or a toilet finishes it's fill cycle, you'll get either a pipe banging or kind of a bugle noise. If this is the case, then it is possible that the hammer arrestors are full of water. Simply turn off the main and open the highest faucet in the system should do the trick. Once most of the water has stopped flowing, close all valves and open the main again.

dj1
Re: This noise is killing me!
dj1

I think that it's related to plumbing, but I'm not ruling out other sources yet. Turn your main off for a few hours, empty the toilet tanks and see if this noise returns.

If it does return, it's not related to the plumbing.
If it doesn't return, post back.

dj1
Re: This noise is killing me!
dj1

I read the posting again, and I see that you mentioned that shutting the water made no difference.

Try this then:

Shut off the supply water to one toilet. Can you hear the sound? If no, there's your problem. If yes, do the same thing to the other toilet (assuming that you have 2). Keep in mind that if your angle stop valves don't stop the water 100%, this experiment can't succeed.

Report back.

kbpepperell
Re: This noise is killing me!
kbpepperell
dj1 wrote:

I read the posting again, and I see that you mentioned that shutting the water made no difference.

Try this then:

Shut off the supply water to one toilet. Can you hear the sound? If no, there's your problem. If yes, do the same thing to the other toilet (assuming that you have 2). Keep in mind that if your angle stop valves don't stop the water 100%, this experiment can't succeed.

Report back.

We did try shutting the water off but only momentarily when we were trying a dozen other things to try to find the source. We will try turning off the main and emptying the tanks as one of our approaches. After another night with sleep lost, I'm open to all kinds of suggestions!

Fencepost
Re: This noise is killing me!
Fencepost

Does it happen a few minutes after the A/C has stopped running? If so, it could be the refrigerant in the system slowly escaping past the expansion valve from the condenser (the coils in the outside unit, the high pressure side) to the evaporator (the coils in the inside unit, the low pressure side). In some pressure range, it makes noise. This could indicate a faulty expansion valve.

You say that "Kicking the a/c on to blow air is the only thing that stops the noise." Doing that changes the pressures in the system, which changes how refrigerant passes the expansion valve. When the pressure differential between the condenser and evaporator sides is high (when the compressor is running), it doesn't make noise. When pressure differential is very low, it doesn't make noise. When the differential is within a specific range -- as the system is bleeding off pressure after the system stops -- it makes noise. This noise is the result of the velocity of the refrigerant passing some restriction.

This noise "telegraphs" through the refrigerant tubing into the evaporator coils which are inside the furnace plenum. Because the coils are fastened to the plenum, it vibrates the plenum, transferring the noise throughout the house.

Your system may need a new expansion valve. Or there may be some other restriction in the system. It could be a kinked refrigerant line. It could be debris from a failing compressor blocking an orifice (in this case, the system would need to be flushed).

I'm not an HVAC tech, this is just my guess. I could be wrong.

dj1
Re: This noise is killing me!
dj1

I was wondering what finally happened with this noise.

kbpepperell
Re: This noise is killing me!
kbpepperell
dj1 wrote:

I was wondering what finally happened with this noise.

Unfortunately, nothing yet. It had stopped for a few days and just started up again. The problem is that it keeps happening in the middle of the night when we're too groggy to try running around or in the middle of the day, when my husband is at work (like just a moment ago). I need him to give me the run down of steps I should try.

I'm going to start with the circuit breaker. Then I'll try the water main and toilet tanks.

I'll be back with an update asap. Thanks again to all who have weighed in!

kbpepperell
Re: This noise is killing me!
kbpepperell
Fencepost wrote:

Does it happen a few minutes after the A/C has stopped running? If so, it could be the refrigerant in the system slowly escaping past the expansion valve from the condenser (the coils in the outside unit, the high pressure side) to the evaporator (the coils in the inside unit, the low pressure side). In some pressure range, it makes noise. This could indicate a faulty expansion valve.

You say that "Kicking the a/c on to blow air is the only thing that stops the noise." Doing that changes the pressures in the system, which changes how refrigerant passes the expansion valve. When the pressure differential between the condenser and evaporator sides is high (when the compressor is running), it doesn't make noise. When pressure differential is very low, it doesn't make noise. When the differential is within a specific range -- as the system is bleeding off pressure after the system stops -- it makes noise. This noise is the result of the velocity of the refrigerant passing some restriction.

This noise "telegraphs" through the refrigerant tubing into the evaporator coils which are inside the furnace plenum. Because the coils are fastened to the plenum, it vibrates the plenum, transferring the noise throughout the house.

Your system may need a new expansion valve. Or there may be some other restriction in the system. It could be a kinked refrigerant line. It could be debris from a failing compressor blocking an orifice (in this case, the system would need to be flushed).

I'm not an HVAC tech, this is just my guess. I could be wrong.

This is interesting. The noise does not seem to be related to the a/c having recently run. In fact, it has happened when the cooling has been turned off on the thermostat. However, it always stops when the a/c starts running...but not if we just try turning the fan on. We had tried just switching the fan from auto to on to see if that helped but it didn't. So, it does seem that the cool air, or something from the a/c compressor, is the release needed to stop the noise.

My cousin is an HVAC guy and with 3 little kids he's hard to pin down but he'll be here for a party on Saturday...I'll definitely discuss this idea with him.

Thanks so much! Kristine

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