1996 Saturn SL2

Something is locking up and ruining the belt. Look for a pulley that is not in perfect alignment with the others. It could be turned a little in relation to the belt, or it could be leaning out a little. It's normal for the tensioner pulley to bounce back and forth a little, but an inch might be more than normal. You might want to remove the belt and spin the pulleys by hand to see if one is tight. GM has had a huge problem with their generators. Beside the far-too-common electrical failures, it is also real common for the bearings to lock up and cause the belt to shred.

Just to add to this one if all the pulley's move freely and the pulley's are aligned and the tensior is still rattling it could just be that aftermarket belt tenisor. So do you mainly hear the rattling when in drive at idle with the a/c on?Also what brand belt tenisor did you buy?What brand belt and belt number do you have on there?As far as your overheating and the gauge not reading hot sounds like you have a bad coolant temp sensor really common on those cars. There only 10 also inspect the connector going to it if it's corroded you will have to replace the connector too. The sensor is located right below where the upper radiator hose connects to the head. There is two wires going to the sensor a black one and a yellow one. The older sensors had a plastic tip that cracked and leaked coolant into the connector corroding it. Let me know what you find.