Noisey Air Conditioner

Hi guys, My Fronty has been making a really annoying scratchy/hissy type noise from the AirCon whenever I turn it on. You dont hear it from inside just notice it when idling in the driveway warming up. I've been to an auto fridgy and he said the coil or clutch may be on it's way out. something to do with the cooling fins within the compressor unit? he's talking 4 figures for repair/replace mainly labour component and even more to fit a whole new compressor. It still works fine but he's saying that continual use and wear will result in overheating compressor which will lead to full replacement. SOund reasonable? Anyone else had the same problem, is it easy enough to find a replacement from the wreckers fit it myself and have someone re-gas it???

Any comments would be appreciated.

Thanks
Doowrag