I'm baaaaack!!!

Hi guys, well I need to tap into some of the vast knowledge on this site once again and I appreciate any and all input.

Over the last couple of months at random times I have noticed after driving my car for a while, errands, or on freeway etc, If I am driving along and happen to have my window down I will hear a dull "clickity clack" or knocking sound when the engine is reving down. The sound makes me very nervous and irritated. So I have been obsessed for the last couple days since I noticed after a long drive that had me over an hour away from home in snowy weather.

So in the last day I have narrowed one fact down, the noise appears weather the car is moving or not, and it happens at an RPM range of about 900 to 1100. And if sitting still in neutral you can hear the noise both going up in rev's and coming down in rev's. BTW the car has 115,000 miles on it.

On my 87 560 SEL I found out there was a chain tension adjuster? that needed replacement and the sound went away. On this car I do not see anything that looks like that.

All other aspects of the engine and performance seem fine, the noise is clearly not present on cold starts and its clearly not lifter noise. It really does sound like a chain or something slapping against another part, it has more depth to it that lifter noise and more of a clunk type tone than lifter noise also.

I sure hope this description triggers something out there and even more I hope its not some major expensive fix.

 

I would have to hear it but I have had some 112/113 engines with a carbon knock, caused by the carbon deposits on the piston and valves. If this is it, I recommend using GM top engine cleaner which works great and will smoke out everything behind the tailpipe and can cause some damage to the catalyst. I think it is illegal in California but works really well at breaking up carbon deposits. Like I said, it's difficult to tell without hearing it. Hopefully it is not a stretched timing chain or something else affecting timing.

 

Hi Guys,

Just wanted to update, I have had a chance to listen closer to the noise and it turns out its actually emitting from the cars mid section, perhaps part of the exhaust? Rattling? Does this ring any bells? Guess I will likely have to pay someone to put it up on the rack and try to track it down that way huh?

 

Extremely common that one of the four catalysts is rattling. Good luck

 

Thanks MBTECHINFO, I shall indeed plan on having the car lifted and get that check, also I have been told to check for rattling heat shields.