Auto Air Conditioning & Heater Repair: 2001 suburban ac tensioner, spring tension, step down

Question
makes a rattling noise when ac on at 1500 rpm  changed tensioner 3 x from dealership and still cant fix the problem

Answer
HELLO LUIS,DID THE DEALER CHANGE THE BELT? IF NOT STEP DOWN ONE SIZE FROM THE ORIGINAL LENGTH. IT WILL INCREASE SPRING TENSION WITH A SLIGHTLY SHORTER BELT.IS THE COMPRESSOR MAKE ANY KNOCKING NOISE?
I NEED MORE INFO TO ASSIST YOU..

GOOD LUCK,DAVIDT