humming sound from the boot
The vacuum pump on my C180 is situated behind the liner on the right side of the boot wall next to the petrol filler inlet. You can only see the pump if you pull off this liner. A few tubes come out of it to operate the door locks, the rearheadrest release and a few other things. The fuel pump/s is situated under the car near the right rear wheel on my car. Cheers.