knocking noise when in reverse or when the A/C is on.

Yes the SL1 saturns with aftermarket belt tenisors will knock like your saying.The SL2s with aftermarket belt tenisors dont knock.I have tried different brands etc on the SL1s and they all knock.With the way the belt routes on the single cam engines causes the aftermarket belt tenisors to bottom out and knock.

So what type of belt should I get, Do you have a picture or website for it? Thank you

Its just a poor design of the aftermarket belt tenisor with the way the single cam engines belts route the aftermarket belt tenisors knock.When there in gear or with the ac on with the twin cam engines which uses the same tenisor they dont knock.I have read blogs about using a certain part number dayco belt tried it still knocks.I have a 1995 SL1 with a aftermarket belt tensior that has been knocking for many miles.The only alternative is to get a factory belt tenisor that looks just like your orginal one.There expensive though thats why mine is still knocking.

Alright then, There's junk yards around here I can go to and get like 2 of them for cheap. Alright thanks Saturntech, I've read all your answers on here and they have helped me a lot.

Your welcome glad i could help you out keep me posted.

Alright I replaced the belt tensioner with the metal pulley with a tensioner with a polymer pulley. I think it is the shape of the pulley that is causing the knocking noise. The new one I got is shaped like the old assembly but the pulley is bigger but I haven't heard any knocking so its great.

Glad to hear you got it all figured out.