Belt to long or to short? What lower crank pulley are you running?
Stock crank pulley. All the rest of the pulleys are stock, also.
Interesting "experiment". I dug thru the trash pile, and found what appears to be the OEM belt, complete w/ GM pt #. I put it on, marked the tensioner where the indicator sits. Dead on in the middle, from the rt hand hash mark.
Removed it, put the new belt on, hash mark moved all the way to the left, in between the 2 hash marks.
Called the AP guy. He said the new belt was .7" shorter. He also said the "belt rep" had told him that moving the tensioner to a higher load, using shorter belts, can/will cause noise. My thinking: Use of a belt that puts max load on the tensioner, & off the "sweet spot", can cause it to deflect, and run the belt toward the ft of the pulley. The new belt is worn on the ft edge.
He has a new, same length belt. I'm going to try the old belt, then a new one. If it works, I'll just keep the oldie for an emergency.
Bryan, an interesting use of a 4 rib belt!
I'll make the tests, and report back.