My 9918 plays music

[Serum]

It's because it gives the motor very much small pulses, in a very small time. I don't know if you have got electric trains running over there, (1:1) but these sound a bit like that too (it's called a chopper, it chops the power in to little pieces and feeds those small pulses to the motor)

It is a nice sound in my opinion..

But are you sure it comes from the controller and not from the motor? The motor has got a mechanical thing (rotor/copperwire) that can create the noise. The controller should nog give a beep IMO.