sounds like you are getting alternator feedback
the charging cable bringing in the power
as opposed to the original cable taking sound to the head unit
I think it is just alternator whine '
just add one of those capacitors to the power line
should take care of most of he problem
I think
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http://www.cardomain.com/ride/30098032004 Limited (Rescue Jeep)
2 1/2 daystar lift 235/70/16
{Electric Stuttertone Emergency Horn}
strobe leds front and rear
2 way VHF radio (kenwood)
westin brush guard+ Hella 500's w/ 100w 3000k bulbs
back seat removed and shelf added
rolled and totaled dec 4 2010..(drunk driver)