when i start the car, sumtimes there is a loud whinning/highpitched grinding/i have no f@#$*&^ clue how to describe it type of noise coming from the rear of the engine, but whats funny it only last for a small amount of time. it stops outta nowhere and u hear a high pitched whistling sound come from the a/c compressor or in that area, and after it stops u dont hear it anymore and every thing runs and sounds fine? im confused