My AC compressor is emitting a chirping sound when the AC is on (but is quiet when it's off), and I'm not sure whether it's the belt, the AC clutch, or a bearing. The noise is coming from the AC compressor or at least near the compressor flywheel.

AC compressor and clutch were replaced with a MC unit about 2 years ago, and the serpentine belt is just over a year old, replaced with a MC belt.

The chirp itself will come and go, when I switch the AC on, it'll be there about 50% of the time. If it does chirp, it will go away about half the time if I cycle the AC off and on. Same with driving, if it starts up I cycle the AC power and it'll go away. It doesn't seem to be effected by engine RPM.

The belt appears to be in good shape, no through or big cracks or delamination. The idler rollers all turn freely, and the tensioner roller turns freely too. The tensioner seems likes it's putting the right amount of pressure on the belt, the belt deflects a little an 1/8 of an inch when pressed hard. I did the soap test on the belt and it didn't change when the sound happens.

The AC blows cold air constantly when on, which from my understanding, if it was the clutch itself it would be cycle between cold and ambient temp air. The clutch flywheel itself is hard to turn when the belt is not tensioned. the AC flywheel does turn when the belt is moving.

I'm stuck at diagnosing the cause of the noise. I'm not sure which parts to throw at it first. Any ideas?