Occasionally when I turn on the AC, or start my '06 van when the AC switch has been left on, I get a a short, loud noise that sounds like belt or clutch slippage/groaning(or worse). It stops after a couple of seconds. Does anyone have any experience or suggestions with this type of problem? It is infrequent enough that I'm sure the dealer won't be able to duplicate it but I don't want to let it get more serious if possible.