I live in Bucks County Pa and recently my heat pump has been making an unusual sound outside. I have emergency heat set to come on at 20 degrees. At 34 degrees like this morning, just as the outdoor unit is shutting off it makes a sound I can only describe as a donkey uttering a death bray. It's loud enough to clearly hear in the house and only makes the sound when the outdoor unit is shutting down after inside temp is reached. What makes this really crazy is it does it sporadically and I know if I call service out it will make the noise.