How long does this noise last?

What is frequency?

What is outside temp?

You have demand defrost or time defrost?

Post model, brand, age of outside HP condenser?

IMO

Thanks for the reply.

I don't know how long it lasts because as soon as I hear it, I turn the heat off.

My wife heard it last week, but then it went away. I heard it yesterday afternoon for the first time, but then I did not hear it again until this morning.

The outside temp now, 11:42am EST, is 37ð, but I don't know this morning's low temp.

It is a Trane XL, about 16 years old.

I just had the tech guy out last month. He replaced the relay because the condenser was running after the air handler turned off. He checked the unit and said everything else looked good.

This post was edited by higgledy on Wed, Jan 1, 14 at 11:49

This is inside the house? If so, do you have a humidifier.

yes, there is a humidifier attached to the air handler.

Dang! I turned the humidifier off, then turned the heat pump on. No water running noise. DOH! Thanks for your help.