Ocassionally when I start my '77 300D a fan starts running immediatly with a slight squeling noise. When I put the shifter into "drive" there is a high-pitched grinding sound. The fan then shuts off as I drive away with no problems. When I put the car back into "park" the grinding sound comes back and the fan starts to run again. This only happens about once a month - the vast majority of the time the car drives like a charm. Any suggestions? Thanks!