I hear it at a very specific throttle position and it sounds like really fast rattling, but disappears completely after a tad more gas. I can replicate it anytime hot or cold. It vanishes with a slight press further, not because of engine noise. Same noise regardless of speed or temperature.
It is definitely coming from the right side of engine (seated in car).

Really odd...Anybody got any ideas?

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

its pinging -- MY GUESS

low octane fuel - worn chains causing an incorrect cam sencer posision as the timing is concerned - if the motor is using oil evey tank full - loose piston #5 for some reason gets loud -

BUT dont worry to much about it unless its make you nuts but you may have to reach deep to start looking for it -- jz

I have a 1988 300 SE with rattling on right side disappearing with throttle advancement. Mine is caused by the exhaust pipe just barely tapping the top of the steering idler arm. You might check your engine and or transmission mounts.

Loose heat shield or exhaust clamps at the manifold?

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1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't

Belt idler shock? These usually rattle with time from a worn out mounting bushing. If it is loose when you push against it, this is a likely source of such a noise.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7