C3500 Rattling (like marbles slowly) stops during acceleration

Can hear it coming from engine compartment upon idle. Stops or gets dramatically reduced when you accelerate. Upon listening under good it appears to be coming from A/C compressor area, almost sounds like it needs some form of lube or something. It also seems to get better upon engine heating up but can still hear it is going very slow or idling. Almost like someone has a hand full of marbles and is slowly circulating then around in their palm.