Mid/Vocal speaker distortion problem?

[Splinter]

Hi, I have a really annoying problem in the fact that, mainly the Vocals and some high end sound on my system are distorting through, I think both, the tweeters on the dash, and the 6.5" speakers. (even on low volume). Any ideas what this could be?? (I may change my amps around, but this still has nothing to do with the distortion)

Setup details:

Rock Fosgate 4 channel amp powering 2 x 10" JL Audio Subs in mono, in sealed box.
Rock Fostgate 2 channel amp powering both Front and rear speakers.
Front speakers are Fusion Mids, Tweeters and Crossovers.
Rear are old OZ 6.5" top quality speakers.
Decent cabling RCA's etc.
TV/DVD control unit in boot from Head unit, (no make/brand)

Could it be the cheap-ish DVD headunit letting the system down? or is it my settings somewhere. Can't figure it out.

Also getting a little bit of 'power' interference, even though I've run power cable down left of car, and everything else down the right side.

[loadedben]

try checking the polarity of the speakers first also check the gain is not turned up to on the amp
as for the interference try checking your earth points or my need a supressor on the live to your head unit you can get one from halfords and are quite cheap