98 honda civic aftermarket radio problem

My wife has a 98 civic ex and the stock radio is only an AM/FM setup. So,
about two years ago we went and got a aftermarket radio w/cd player. They
had to jumper the wire from the old radio and leave it behind the dash so
the keyless entry and dome light will still work. Here is the the
problem....after about a year the radio started getting a high pitched noise
that could be heard all the time and it interferred with the microproccesor
causing the CD player to stop. I just assumed it was a bad radio so I went
and got a new one of the same brand so I could use the same wire harness.
It has worked just fine for about another year until two days ago. the new
radio is doing the exact same thing. At first I thought it was a bad ground
or the antenna was not hooked up right, but after checking the antenna and
giving the radio a dedicated ground it still did the same thing. Oddly
enough the only way I can figure to consistently stop the noise is to
squeeze the radio on the bottom! I even took the radio apart. it looked
fine as far as I could tell.
So here is my question: Is there a possible problem with the wiring causing
these radios to short out? It all looks pretty clean and correct, but what
do i know. I am thinking of getting her the separate cd player that goes in
the bin behind the cup holders. It looks like it just wires directly to the
factory radio with an eight pin connector.

What should I do?
Greg Toft