It could be the gap. I tightened it on my sister's Mystique and the a/c stays on now, even on a road trip. She did not report noises, though. But there could be oil in the clutch or the compressor is failing. Make sure the cooling fan(s) on the radiator are both running and there is no tight bearing on either one. If there is too much a/c pressure from lack of fan cooling, the pulley can slip and you might lose refigerant (sounds like a gunshot!) The clutch assembly is replaceable without changing the compressor.
