I got an W124 from 1991 model 300E-24
It got the M104.980 Engine 3.0 Liter with 24 Valves.

I got this ratling sound at the top of the engine
And the sound can sometimes go from cyl. 6 to cyl. 1 or stay in the midle of the engine, but always from the top of the engine.

The strange thing is that it is only there when the engine is cold and it goes away as the engine get hot.
When driving temperature is reached, then the sound is completly gone.
And the next strange thing is the sound is only there at 1500 rpm.

The best way for you to help me, is to hear the sound for your self.
So here is a link to a you tube video I uploadet.

The sound has been there for the last 10.000 Km. and has got a litle bit worse but not much.

I have resently changed the oil pump and oil sprayers, but that dident helped at all.
A very big job by the way to get that Oil sump off the engine on a M104 in a W124 chassis

300E-24 engine klicking Sound only at 1500 omd/min - YouTube