W124 Fuel Pump Relay???

Hi All

My grandad tells me that he hears a humming sound go on for a couple of seconds after he switches off his ignition on his '89 W124 200E. It seems to come from the fuel cap side of the car.

Could this be the fuel pump, and if so, is it a sign of a fuel pump relay going south?

I haven't yet made time to take look at it to get more info on the symptoms but that is pretty much his worry.

Any help would be appreciated.

Tks a heap, guys.