Turbo or not Turbo

[Simon H]

Don't really know where to start I drive a 2004 C270 CDI 23,000 miles full MB service history I have owned the car for two years. Over the last
couple of weeks I have started to notice a strange noise that appears to be coming form under the bonnet towards the left hand side.
Its intermittent, only occurs under acceleration between 25- 40 miles per hour and is cross between a hum & a whine.The cars performance appears
to be fine. At first I thought it might be something to do with the air con but have switched this off and the noise still appears, I did wonder if it was
turbo related wastegate noise etc and typical for a turbo diesel.

Any advice / help would be gratefully received

Thanks

 

[Dieselman]

Hard to say from your description but it doesn't sound particularly like turbo noise, and the turbo is on the right hand side of the engine bay also.

Faulty turbos normally make more noise when under load so the more load the greater the noise, not necessarily engine speed related.

Can you hear the noise with the bonnet lifted, if so where from?

 

[Simon H]

Haven't tried with the bonnet up, have tried though with the car stationary and couldn't hear a thing, only seems to occur on the move
which did make me wonder if its gearbox related or possibly a wheel bearing

 

[BlackC55]

Is it a flapping belt caused by a alternator pulley giving up?