I have purchased a 90 year-old house. It is large, has mostly plaster interior walls, has steam heat, and many of the original galvanized pipes remain.
Nearly constantly today, I have been hearing a vibration in the house. It is faint, but very distinct. It has been coming and going for two months now, however this has been the worst day of it so far.
* I cannot get close enough to the sound; it always sounds distant. I can get to a point in the house where it almost cannot be heard, but I cannot find a point where it is loudest.
* When the sound is heard the cold water line vibrates. I can hold on to the line where it feeds into the hot water tanks and feel it vibrate. I feel the same vibration at the line coming out of the water meter - although it is not stronger at either point.
* The sound is not linked to any particular event occurring - not the flushing of a toilet, turning hot or cold water on or off, filling or not filling of an automatic ice maker, auto-filling the boiler, boiler on, boiler off - nothing is linked to the sound. I do not think this is a 'water hammer'.
* Sometimes the sound lasts a mere second; other times it lasts 8 to 10 seconds it seems.
* The best description of the sound is a very faint jack-hammer.
* I have turned on every faucet, washing machine, dishwasher, etc and cannot expel air from any line.
* There are two Watts Expansion Tanks installed on the cold water line, just before the hot water tanks and just after a valve I have been told prevents water from flowing backwards. These tanks are pressurized at 50 psi, which I check often. Increasing the pressure in the tanks by 10 psi today has not resulted in any change. My city water source is also 50 psi.
* Oddly enough, the sound usually ceases around 6 pm, and I never hear it at night. I'm waiting to see what happens tonight, since it's been a nearly constant annoyance today.
* The first time I heard this sound followed two events: 1., it started to get cold outside, and 2., I had extensive work done by a plumber, who made a fair number of mistakes. One mistake he made was not soldering joints; another - forgot to turn back on our hot water circulation pump. He completely turned off the water supply to the house several times during the course of his work resulting in many trips through the house to turn on all the faucets and expel air from the lines.
I will be so grateful for any input!! I am desperate to find the source of this rumble. Many thanks.