Distortion only with 2 sets of rcas in 4 channel amp

[caseyarndt 10+ year member]

I have tried several 4 channel amps and still get the same distortion.

When only one set is hooked up there is not distortion on both sets.

But right when the second is hooked up there is tons of whining even if the car is off.

I have tried changing out rcas but same result.

Is it just my deck? Rcas are all Rockford, grounded headunit RCA outputs, and upgraded hu ground wire.

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