I dont have any clue about this aspect of the car. (Under the hood) and EVERY time I am in Idle, there is an awful almost grinding sound. A/C does make this sound a little more dramatic however it is absolutly awful at all times. Usually it stops once I start to accelerate from a stop... Usually.
So..
1. Grinding?
2. A/C?
3. USUALLY, only durring idle and reverse.
4. Sometimes ALL THE TIME.