Pulsating humming sound when using A/C
So since this is the first time I've had my Jeep where it was warm enough to use the A/C, I figured I'd give it a shot. It is nice and cold, and I didn't realize this until I got home and the engine wasn't making so much noise, but there is a pulsating humming sound that sounds like its coming from under the driver seat. I popped the hood and got out and couldn't hear it unless I was in the car. It is the automatic style controls, and when I turned off the A/C compressor (using the snowflake button) the humming stopped. It is very repetitive, maybe in a sequence like this: "hum for 1 sec, silence for 1 sec, repeats".
Any idea what this is? Low on coolant? Needs a new clutch?
Let me know if you need more info, thanks a bunch!
Oh and its the 6cyl engine, if that helps.
1996 Jeep Grand Cherokee Limited Edition 4.0L
3.55 axles, stock pretty much everything, except for a PSC steering gear and fuel injectors