1990 300SE
Engine 103.981
Chassis 126.024

I am hearing a rattling sound which I perceive to be like the sound of the timing chain rattling against the guides maybe? This noise is heard not just after starting up, but continued to rattle minutes while listening to the motor idle. However, when a friend revved the motor up to maybe 1500 RPMs, the rattling stopped. I tried to locate perhaps a loose piece of plastic as the cause but had no luck in doing so. I have read a few threads in this forum regarding the timing chain being strong on these cars (I only have 125000 miles), but could the tensioner be bad? And if I am going through the process of replacing the tensioner, assuming that is the cause, shouldn't I just go ahead and replace the timing chain and all the guides also?

Thanks in advance,
Michael C.