Sorry, I'd missed that part before.

That's very VERY interesting that the line-out plugs are fine but the docking connector is bad. This means that the hardware fault is very limited. Maybe something as simple as a dirty or loose contact on the docking sled connector. Maybe you don't need to send this to Stu after all.

Are you using four channels, or two, from the docking connector? Is it both the front and rear outputs on the docking connector that have this problem, or just the rear? If it turns out to be just the rears, and you weren't using them, then just swap to the fronts and fugheddaboudit. Or look closely at the docking connector connections. You can even pull them out of the connector to inspect them, assuming you know which one is the suspicious one. (Linked movie file shows the sled side of things; if checking them, check both sled and player side of things. Remember the wiggly docking connector feature when working with the player side of things.)