A23 AMP

If the amp hums with just speakers connected and no inputs. The problem is internal and Parasound should take care of it under their usually prompt warr. service which is still in force. 5 months sound odd. Was your dealer getting it or was it direct?
If not them connect one component at a time, add preamp next(nothing connected to it). If it hums them use a 3-2 ground lifter on the AC cord of the amp and do not connect the wire to the outlet screw.
If not them connect each component. If you have cable very often this will cause hum even if you are not listening to cable sound. Use a ground isolator in line with the cable RF input.