This problem relates to a 1991 (August 91 registered) W124 300TE.
If you have the interior light switch on the dash, set to the 'come on with the rear doors and boot open' position, you'll get a strange buzzing from behind the dash (which sounds like a slightly strangled lights on...
I've bought a used c class from mercedes which was about 10 months old c180k, on the 53 plate.
Problems, pulling to the left - cured after three visits and they had the car for more than 2 weeks.
The drivers side window is making clicking noise on open/closing it.