I suspect the hum is a PC style cooling fan inside the housing that is used to vent warm air away from the PCB. Any ideas what that is in the upper right corner atop the black case (click here
for a bigger image)?
The lack of an on/off switch is very surprising as up until the Neo, Tacx had always had a switch to power off the motorbrake for the powered trainers. In this case, Tacx recommends unplugging the trainer when not in use but I would imagine a better/preferable option would be to plug the Neo into a surge protector/power strip, and then turn off the power switch when finished.