Myth. DC cannot induce noise into AC through EMI.keep your speaker level wires, all wires really, away from the power wire. No parallel runs of signal and power lines.
Well , I have the Nav one LOC here i could hook it up,, but I didn't knwo they caused such a problemI've never had any luck with them. IF all else fails, try a high quality LOC. I had this same problem in my girl's car and no matter what I did, I could not solve it. Finally broke down and spent $35 on a Navone LOC, and that solved the issue. I wish I'd have done that from the start. Would've save me time and frustration.