I'm baaaaak!!!

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 960 to 1,100. And if sitting still in neutral you can hear the noise both going up in rev's and coming down in rev's.

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.

Thanks guys!