i have a prolblem with ac/defrost system when ever i turn on something that uses the compressor some times it will catch and sometimes it will slip and make this farting noise. i just replaced the belt with a gator back could this be just a weak tensioner or a more serious prolblem. i tried letting some of the pressure out of the ac system and that seemed to help but this still does it some times. the car has 75k on the clock

Its either a weak tensioner or the A/C compressor is locking up.