Well, I understand all the suggestions to send the unit back, but the seller is eager to make this right.
Stopped by HEAR today, spent 2 1/2 hours with Ben and we found the failure. Apparently ARC never considered the possibility of rough handling during shipping. The output coupling capacitors are tied together using what I would assume is some sort of foam backed double face tape so they form a single group. They are not anchored to the pc board by anything but their leads. If the unit (new or pre-owned) is dropped on the side ignoring the Fragile This Side Up labels all over the box, then they move as a group and depending on how hard a drop and the number of times the leads break. This is what happened in this case, two capacitors leads broke, one on each channel, so that was the hum in each channel.
So two caps will need replacing, as while I was there he de-soldered the four caps and now it is just getting the parts in and installing. He will make a minor modification to attach the caps to the board to keep them from moving....a bad design for a group of caps with some weight behind them when they are fixed together.