Well that's a bitch if true. Although...using the same signal path of RCA's to the back, when I use just the HU with no line driver after it, I don't hear the noise. Which would make me suspect that the either (A) The noise is just below audible level and when gain is boosted, I'm pushing it into that range, or (B) the line drivers ground isn't isolated and/or the unit has an issue? I suppose the best way to test would be to connected it to a separate power source like an external battery and see what happens...? Thoughts?