What is causing the loud screeching noise when my A/C shuts off?
It could be a leaking discharge valve or reed on the compressor. When the compressor shuts down the head pressure pushes past the valve. If the unit has service valves, shut off the discharge valve out of the unit, run the compressor until the head pressure increases to it's max, shut off the compressor and listen. Any good service tech can do this. If there are no service valves, then I would run the unit, shut off the compressor and use a stethoscope to listen to the compressor. If it is not the compressor then use the stethoscope on the reversing valve. Check the fan bearings to make sure it is not the culprit. And while you are at it go find a good service tech and never call the other 4 imposters.