I notice you're doing the power and ground runs for the two components (empeg and amp-- the CD receiver IS the amp) two different ways. Something as simple as different wire gauges or even different wire lengths for the two runs can cause a ground loop.

You might want to re-do all power and ground wiring for both units, using heavier gauge wire, where the gauge is the same for all runs on all components. And make sure they're both grounded to the same point, and both getting their constant power from the same point.