Your mechanic is right on the dot!!!

My cousin's 300TE has exactly the same problem, it is a whining noise which fullfils the interior of the car as, you said it, a whine from the radio. It increases as engines revs increase. It is a very different whine from faulty belt tensioner or transmission whine.

It is a faulty hydraulic oil pressure for the rear self-levelling suspension. Pump appears to be involved too. The diagnostic was done by the local M.B. dealer and fixing it requires about two thirds of the Blue Cross annual budget.

The dealer said that if you can live with the noise, do it until the system fails completely. The cost to repair it would be the same at any scenario.

__________________
A. Rosich
CL 500, 1998
S 500 L, 1998
E 320 T, 1995 [Sadly sold ]