Crpiecho

I have 2000 jeep Cherokee with about 119 k on it. Recently when I start it up at idle I hear this sound almost like water/fluid being tossed around and there is this weird vibration. Then it goes away well one day I caught it while the hood was up and the ac compressor was the source of the sound and it was shaking a bit. Haven't had the belt off to see of the bearing or clutch is what is causing it but what else could it be with the compressor,,,,, low oil/low r-134a ? The ac still works and it doesnt make any squealing sounds when the ac is on besides when
I first start up due to tightness of the belt.

I don't have any experience with ac systems on cars. About the only thing I haven't done myself