I have a 220TE (W124, 1993) and when I switch on the ignition there is what sounds like an electrical/electronic (it doesn't appear to be mechanical) 'buzzing' noise which persists when the engine has started and is running. The noise seems to come from within the dash, but it's difficult to locate it. Any ideas as to what's causing it?

 

I consider that buzzing important although it is a little annoying. The buzzing stops after a few seconds which then you should start the car. Within those buzzing seconds the car gets itself ready in other words. But I don't know how to turn it off...