problem with stereo setup

Hey everyone,

I just installed a system from my high and lows.  I have a 89 240sx with a 2003 Kenwood head unit, lightning audio amp and soundstorm 4x6s.  Now the problem that I'm having is that when I hookup the rca cables straight to the head unit and amps I get a popping noise when power goes off and an alternator whine.  So I purchased two ground loop isolators and hooked them up and now all the noise is gone although it took some of the music away with it also.  Its like I'm only getting the instrumentals and no voice.  What should I do buy new ground loop isolators or buy a new head unit or what.?

i have the power wires on one side of the car and the rca running down the middle of the car.  I had an old set running on the opposite then I bought new ones thinking that the old ones were bad and still have the same problem.  I could try moving the new ones over some more. 

thanks

aric