When my engine is warm and at idle my belt squeaks like crazy. While you are driving or at anytime when the engine is cold you don't get any noise from it. I have replaced the belt as it was getting worn but I have not done anything else to it. I would assume it is something wrong with the idler pulley but I my wife said I had to post on here before she would let me do anything to it. I have googled it and most people were saying to change the belt which I already have done. It is also not nearly as loud as the high pitched squeal that belts make when they are loose and cold.