I swear I have so many problems with the AC in this car.

It is finally working but now when I turn off the AC there is a strange loud noise that comes from the compressor area.

It is a new compressor (year old).

At the start of summer there was amost 0 pressure in the system (cap was broken and letting the pressure out of the low side). I just charged the system with 18 ounces r134 (the kind that has 2 ounces oil and 16 ounces r134). That was not enough so I added another about 6-8 ounces of just 134 (no oil). I have been told that a lot of the oil stays in the system when there is a leak so I added some that did not contain oil. Could a lack of oil be making that noise? I mean it at least has 2 ounces so even if low it shouldnt make that noise, or is there a flaw in my thinking?

In searching I see that could be a loose belt but would that only happen when the ac is turned off?

Thanks all.