Audio Systems: Car radio antenna, car radio antenna, car chassis

Question
Hello there.

I got an american VR3 car radio (Virtual sound www.vr-3.com) and I live in Europe.
I had to install on a car that has not been provided with a built-in antenna so I added an antenna.
The problem is that when I touch the metal parts of the vehicle with the ground wire of the antenna, I get sparks.
I noticed 12V output from the device and I'm wondering if it's OK to have 12V on the wire that I have to connect to car chassis.
Is it different for american car radios?

Thanks in advance.
Elis D.

Answer
somethings not right there, there should be no voltage coming from either the shield of the antenna or the center wire.  it is possible to have .5 volt or so difference on the shield but that shouldnt make a spark and certainly shouldnt be 12v!!!
answer these questions for me please
Does the cd player work fine without the antenna connected?
does the anntenna show any voltage between it and chassis when not coneected to the stereo?
Is your car a posative chassis or negative?  there are a few cars that use the posative for their chassis and this would cause this problem since american antennas are grounded.

Let me know.