Maybe its an issue. maybe not. I noticed the other day when idling in park and the AC was on-- when the compressor would engage it would make a low pitch thump. I could actually feel it in the floorboard. I thought it was actually someone shutting their door beside of me but when it happened again i turned the air off and it stopped. Is this a sigh a compressor, pulley, or bearing is going bad with AC or is it normal?