Hi guys, posted in the CLS section, but figured i might as well ask here in the tech forum also.

Please help me identify an engine noise coming from my recently aquired car.

The car is a 350 (M272 engine), model year 2004, 70,000 miles on odo.



The noise is a medium-pitched whining sound.
It starts after accelerating to about 25mph, most noticeable at 30mph, but still audible at higher speeds.
Always the same pitch, non-rpm dependent.

Does not change pitch or go away when gear selector is shifted to neutral or when manually shifting the auto-gearbox up or down.
When it has started (accelerating to >25mph), the sound is present even when deccelerating down to 15mph, when it fades away.
It is not affected by the AC or fan settings.
It does not change when steering is in full lock.
It slowly fades away after approximately 20 minutes of driving.
No OBD-error codes.

 

maybe engine and tranny mounts?