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Ever since I installed my second amp I get an awful alternator whine from the speakers. Last night I believe I finally isolated the problem.
First here's my setup in case it helps:

Pioneer DEH-4100UB Headunit
Kenwood KAC-8405 powering:
Infinity Kappa 60.9cs Components in front
Infinity 6022i's in the back
Kenwood KAC-8104D powering:
2 Kenwood KFC-W3012 Subwoofers

After installing the KAC-8405 to power all four of my speakers the whine started. It rises and falls with the engine, so its obviously the alternator. Last night while attempting to ground my preamp outputs on my HU to see if it fixed the problem, I discovered that I only hear the whine when the middle pair of RCA's are plugged in. I have three sets of preamp outputs (1 to my sub amp & 2 to my 4ch) and I switched them back and forth until I isolated the problem to the middle pair. It whines regardless of which pair of RCA's are plugged in. It also whines when the middle pair of RCA's touches the metal on the back of the radio.

So my question is: Is it a bad middle RCA cord? Or should I be using one of the cords that splits from 2 inputs to 4 outputs? Thanks!
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