Clk 270 engine noise

[Leighton 270]

Hello all I have a 2003 clk 270cdi auto. ,130,00 miles.
I have just noticed that it has developed an engine noise at 2,000-2,500 rpm when on light constant throttle. It is worse when cold, i first noticed it in between gear changes, as the auto box changes up. It pulls well and thertre is no smoke. If you drive it hard there is no noise. It sounds like crank or diesel knock. Any advice would be great full.
Thanks Leighton

 

[mersum1es]

Noises are very hard to describe, but often these are injector based. With star diagnose system you could see live data (correction values) under different load conditions. Also injector leak test (at idle) could give a hint about worn injector. Leak test is pretty easy DIY (use search).

Cylinder compression test could reveal if there is incomplete seating of the gas exchange valve, I remember one case in Finnish MB forum where that was culprit.

 

[tec]

The 270 engine is not exactly quiet.

Can you record the noise and upload it so we can hear it?