Hum is kinda normal and could possibly be quieted with paper, wood, cardboard wedge, silicone, etc. It is usually the metal plates being vibrated at 60 times per second (60hz is our normal ac rate stateside)
To put our voltage in a somewhat comparable perspective; 9v batteries tingle or sting your tounge, Your sweaty arm across live rails at 15v-25v has a similar effect, needles or pokes on the forearm, 50-75v is about what the doctors use for those muscle contracters in muscle rehab and where your fingers may begin to shock a little. Over that is painful. Huge amps and lower volts can be an issue welding, etc, but not much concern to model RR folk.
Most folks are taught to fear it as a kid and never get over it.
