My Kenwood stocker HU lasted about 6 weeks before taking a dump. The RCA pre outs got loose and I'm fairly sure that the entire board became loose/shorted which in turn caused it to pick up all sorts of static, altenator whine, blower whine, wake plate noise etc. I wound up with another Kenwood as my wired remote, satellite radio and iPod box were all Kenwood, but probably won't purchase the brand again when the time comes.
Get a 3.5mm to RCA wire and plug your iPod/mp3 player directly into the amp and see if it still does it. Very simple test to see if it is the HU.