Guitar Feedback sound at 60-70MPH

[airbag]

Hello,
My 2001 C320 estate has started to get a sort of "guitar feedback" hummmm sound when under acceleration at approx 60-70 MPH. It could be wheels or rear axle area I think.. just wanted to ask for any opinions first before taking in for diagnosis. When I button off the gas, the sound does dissapear, it does not seem to change pitch at all and is very much like a guitar Amp sounding feedback noise.

Thanks for any assistance.
airbag.

 

[Bolide]

Sounds like a worn diff

Nick Froome
www.w124.co.uk

 

[brandwooddixon]

I'd check around the exhaust first. At least while you're at it you can check for oil leaks around the diff. casing.

 

[airbag]

Thanks for the replies.
Worn diff... eekk!

Shes only done 46,000 .. so I would be surprised if that is the case. Still seems to be getting worse after long runs, so I will take it in for checkup.
Thanks for taking the time to reply.
airbag.