Definately a scary sound when the car makes unusual noises. Car noises can make anyone feel nervous. Brakes squeal can be dangerous and engine knocking can be very bad. Another bad noise is when you get a whining or grinding noise when you turn on the Car Air Conditioning.

There are a number of reasons that you can get noise. If the noise only starts when you turn on the Climate Control and your vehicle A/C is clutch driven, then the bearings in the clutch have gone bad. You can try and replace the clutch, but most likely have to get a new AC Compressor and it will have to be changed. If the system does not have a clutch, then the compressor will definately need to be changed.

If the noise is constant then more research needs to be done. You need to be very sure it is coming from the ac compressor. If it is a always on system like some late model Denso Compressor then the compressor will need to be replaced and the system serviced.

The key thing to be checking in the case of compressor noise is head pressure. If a compressor builds up too much pressure the heat will cause the clutch to melt and the bearings to warp. This will cause lots of problems and make for a noisy system. Do not put on a replacement reman ac compressor without determining the cause of this head pressure. Usually it is a blockage in the system, problably at the condenser and it should be replaced as well.