1995 SL2 1.9 DOHC
I have a knock that develops when the AC is turned on. It sounds like the belt tensioner it slaping against its stop. I have heard other saturns with the exact same problem. Sometimes i slap her in neutral at stoplights to get rid of the noise...I'll try and post a video today if anyone cares to chime in...

 

When the A/C is on .... ?? Your description would more likely fit a loose electric clutch on the A/C compressor itself .....

 

I dunno, thinking back, can't remember many failures of A/C compresser clutches. When did, mostly lost A/C. It just quietly quit running. Generally in the middle of a long run on a 110 degree day. Lost a lot of those belt tensioners though. I can see if parts start letting go it could maybe make a noice like a knock when loaded with an A/C compressor and the engine is running slow enough, as it might be at stop light in gear with an automatic. Although for me it has been OOPS, oh darn, when releasing the tension OR belt squeal.

 

To: QuietFlight & OceanArcher
I had this exact same problem with my 2002 SL1. I determined my belt tension felt normal, which suggested tensioner wasn't the problem. A little research showed a slight difference in belt diameter between two local suppliers, Autozone and Oreilly's with Oreilly's being slightly shorter-2 or 3 mm. I replaced the Autozone belt I had on for close to 2 years with Oreilly's-problem solved. No more clattering!

 

This is a 7 year old post. Both are long gone.

The following is NOT bashing YOU, danrgmc -- it is bashing the stores.
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Yet another demonstration of why NOT to buy car parts, especially saturn parts, at Oreilly's /Autozone/Advanced.
NAPA is passable. They also carry the OEM Gates brand belt that exists to fit Saturn DOHC's and nothing else.
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, visit rockauto.com.