1999 Sebring Convertible Air Conditioner is making noise

big end bearings( lower engine rod bearings to confuse) knock at idle and get louder with rpm
if the noise changes with rpm and you are hearing it near the ac compressor then it could be the ac pulley bearing
test if it is the compressor by listening and then turning the ac off the pulley will still spin but the compressor stops
if the noise remains , replace the pulley bearings

Check the belt on the compressor, is it slipping on it ?

This could be the belt slipping or a bearing going/gone in your alternator, air conditioner, steering pump, idler pulley or water pump.

If it is a purge noise the highside pressure may be getting to high and relieving pressure.Usually this can occur if there is too much freon or a restriction in the ac system.The defroster utilzes the ac as well which is why you can hear this. From your description it sounds as if the compressor clutch bearing is going bad.

This problem sounds like the aircompressor pully, the bearing is shot.
With the engine running and the air conditioner off there is a grinding noise, look at the compressor pully, does it wobble? Then turn on the air conditioner and the noise stops, look at the compressor pully again, the wobble stops? If so that's the problem.

bearing in ac pulley is faulty

chances are there is a bad bearing, inside the air conditioner compressor. where the belt goes there is a centrifugal clutch, listen close to there and if's from there, you need a new compressor.

the compressor clutsh is gone , you will need a new compressor

Could be several things. WHICH ENGINE?.. 4 cylinder (has three belts, power steering/water pump, alternator & A/C compressor, one tensioner pully A/C compressor), The V6 2.7 (has only one belt, 1 Idler pully and 1 tensioner pully), the V6 3.5 has two belts - A/C/alternator, and power steering - there are two tensioner pullys). Noises can be caused by the belt(s) themselves, pullys, bearings, pully bearings, water pump shaft bearings (or belts/pullys rubbing up against something). Let's not forget that there is also belt(s) behind the Timing Belt cover as well as pullys and bearings associated with the timing system. You could start by removing one accy drive belt at a time (alternator, water pump, compressor, power steering, etc) to see whether or not the noise goes away in each case. If after each case, you discover the noise is still there, it's probably behind the timing belt cover (idler/tensioner pully, water pump shaft bearing, crankshaft bearing, etc.). Good Luck

clutch bearing on the a/c unit or there is belt shredds in tn behind the front part of the clutch..