I have a Trane XE1000 heat pump that is about 10 years old. There are electric heat banks for the backup auxillary heat. Just recently I started noticing a humming/buzzing noise (that is clearly audible through the vents) when the heat is on sometimes. Here are the times that the noise seems to be around:

If the temperature is lower than 40 degrees, the noise occurs when the regular heat is running for the first minute or 2 before the noise goes away.

If the temperature is lower than 40 degrees, the noise sometimes comes back (the regular heat is still running) about a minute or 2 before the heat kicks off (because the temperature that the thermostat is set on has been reached).

If the temperature is greater than 40 degrees, the noise does not occur when the regular heat is running.

If the auxillary heat is kicked on, the noise will continue as long as the auxillary heat is running.

With both the regular heat and the auxillary heat, the air output temperature is what it should be in both cases.

The noise appears to originate somewhere near where the auxillary heat banks are located but I didn't want to start tearing things apart until I had some idea of what to look for.

Does anyone have any ideas on what might be causing this noise and what to check?

Any help would be appreciated. Thanks!

 

Feel around the coil there and see if you feel it in the lines there where the bypass and TXV valve is. When was the last time you had it serviced and gas checked?

ED

 

I will check that out tonight after work. If I do feel this in the lines, what does that imply the problem could be?

Everything was serviced very recently and ATT it was given a clean bill of health.

 

Still lots of things. The big line should be hot in the heat mode and goes through the coil them a by pass around the TXV . There is like a check valve there that does this. If they checked the freon on the AC. It could still be the freon in the heat mode.

Ed

 

One thing to check is to make sure none of the refrigerant lines are not touching each other or the heat pump housing. This can cause more strange noises than you may think possible.

 

I think you may have a defective relay with a bad holding coil on one of the strip heaters. Unless the unit has none,...most do.

 

My vote is for a bad contactor too. Been there, got bit by it.