Just got my car back after a service and brake pad and disc change and i have noticed a low pitched noise coming from the back of the car (sounds like it is inside the car) and is always there when the car is running (i.e. does not have to be moving) i have noticed that the noise is the same noise you get for 2-3 seconds when you click the ignition on.
Any idea what this noise is? could it be the fuel pump?
Any advice would be very helpful