What sort of sound the PiCycle™ make?

The PiCycle™ is virtually silent due to the fact we separate the two propulsion systems, i.e., motor drives the front and human drives the rear. So there's no internal gear meshing, which in other bikes can result in a whine. Also, the patented bike drive system is completely silent. While riding you will probably not be able to hear the very quiet noise from the motor.