I am having a heat pump issue also. This morning my heat pump made an ungodly loud noise. I called someone who told me that this was just the unit going into defrost mode. The sound the unit made was loud enough that the neighbors heard it. I don't know if this is normal. I shut the unit off and restarted it later and it started heating with no problems at all. Does anyone know what this could possibly be? I don't know if this sound was really just the unit defrosting or if it was something else. I put my hand on the suction line once it started back up and it was warm and the unit was producing warm air. I can't find anything else online about a noise this loud. It was way more than just a humming noise. Does anyone have any thoughts?