I had a whinning sound coming from my electrical fuel pump that below the rear seat under the car. The technician suggested to change it plus the hydralic pipes and the filter that's beside it. Mine is a W210.
I'm trying to justify to myself for the money spent that it gives better power output after changing it. Does anyone have similar experience on this? By the way, does the car breakdown half way down the motorway or it is just a tell tale sign that time's up to change?