go to radio shack, buy a ground loop isolator for like 5 bucks, wire all your audio system grounds to it.. if you ever get a video screen, hook that ground into it too.. nothing worse than getting ground loop interference in a screen... you het horizontal lines running across the screen whenever you rev.

 

if your subs are putting out 2kHz than you are doing something wrong. my subwoofer puts out nothing above 100Hz. you should leave the 200Hz and above range for mid-bass. the 2kHz range is still in the voice range.

 

i have my headunit grounded behind the dash to a bolt, the ground wire is about 8" or so. my amp is grounded to a bolt in the trunk for the gas tank, the length on that is about 2 feet. optimally you should not have grounds more than 18", but definitely not longer than 5 feet. all the amps should be grounded at the same place. since the stock headunit doesn't have a ground wire, just make sure the area you ground it to is very clean.

also make sure you run your power cables on one side of the car and the RCA cables on the other side. that is important too.