Ok I have an 04 Grand Caravan and when you are sitting with it in drive and at a compete stop there is a rattle/vibration type sound coming from around the compressor/waterpump/idle pulley area. It will go away with when you turn off the air or if you give it just a couple more rpms with the a/c on it will go away. Kind of has me puzzled. Doesnt do it driving down the road or even at idle if you are in park

 

Welcome to DF
I would pull off the drive belt and inspect all pulleys and the belt tensioner. Also tighten the a/c bracket too.

 

I took off the belt off and it seems there is a small amount of play on the water pump pulley , Im going to replace the belt and tension and idler pulley first then the water pump later to see what happens