We have a high-pitched noise coming out of our heating vents. I can not hear it, but my wife hears it clearly. It is a continuous high pitched whistle even when the heat is not on. I turned off all electrical power, water, and gas to the house and released pressure on the gas and water. The noise continued. I disconnected all smoke detectors and removed their batteries and the noise continued. Our HVAC guy hears the noise, but can not locate it. The heat pumps are 14 years old. The noise started this autumn and has continued for at least two months. Any ideas on how to locate this noise? Is there a noise detector/meter that might help? We really do not want to move. Help.