System was running normal when I got to it. It had no loud noise or knocking. Ran the heat pump on test mode and it ran fine, it produced 22 degrees of heat. Forced it into defrost and it sounded normal didn’t see anything wrong. Tested heater banks and all came on. Blower motor ran fine while testing. Filter looked good and coil had no obstruction. I could not replicate what the customer had heard. Everything is working well at this time.