humming noise

I have a r107 1979 and recently have noticed there is a humming electrical noise coming from just in front of the gearstick in the central console. Bizarrely it stops when i put the indicator on. Does anyone know what could cause this? Many thanks

I had my car serviced by a Mercedes Benz dealer and it has come back with a humming noise. The dealer is insisting that that the noise was already there but that is not the case. The dealer is suggesting a change of the fuel pump which will set me back by around 300-400 pounds I took the car...