I've got an annoying rattle that appears to be coming from the serpentine belt tensioner. The tensioner (due to belt length) is right on that fine line between it's max stretch position and just short of that, so the stop keeps tapping at the tensioner body. As the AC kicks on and off, it tends to change just how close this is, and makes the rattle come and go. So I know what the problem is. But I don't know why... I have a Goodyear Gatorback serpentine belt on it now, and it's somewhat new. So the belt should not have stretched to be too long at this point. I looked up belts on Motorcraft, Rock Auto and Amazon and found these references: JK6-867 - 86 7/8" long, w/o High Output (apparently high output A/C) JK6-871-A - 87 1/8" long, 4.0 SOHC and "all engines" JK6-884-HA - 88 4/8" long, 4.0 SOHC apparently with a manual trans Most aftermarket sites call for the JK6-867. Motorcraft's site now calls for the JK6-871-A. Im thinking that the latter number is an updated number, and the original number might have been the 867. Sometimes if two belts are really close in length to eachother, the OEMs will eliminate 2 part numbers and just replace it with one. That's probably the case here. So here's my problem: My Goodyear belt is 86.5" long according to the description. That's shorter than the shortest Motorcraft belt listing. And yet it's too long, and causing my tensioner to bottom out and rattle. Anybody have any experience with this?