I have the same problem with a volvo 2005 s80. the AM reception is both poor and full of static. The copper strip, you heard about, is the supposed solution for the problem. In fact, I found the proceedure to get to the antenna amplifier and found that the strip had alreasy been installed by the dealer. The strip is slipped between the cable connector on the cable from the radio and the receptical on the antenna amplifier. Best I can see is that it simply tightens the connection and keeps it from coming lose. It is not a good fix. The problem remains. AM is still poor at best.
I think that the elements in the rear window effectively act as two antennas. One pointing both front to back and the other side to side in the car. Which ever antenna is giving a more powerful signal is switched to the radio. This is what is ment by diversity antenna. Sounds good but the real problem is that they are using the window elements as the antennas
I removed one of the connections of the antanna amplifier to the rear window antenna elements and put my fingure on it. WOW - instantly I became one of the antennas and the signal was 10 times better. My body was acting as one of tha antennas.
Conclusion - The real solution is to have one of the connections to the rear window antenna elements instead go to an external 31" motorized mast antenna. This mast will most probably always give, by far, the best signal and the antenna amplifier will always send its signal to the radio. I will try to get a roof magnet antenna and set it up this way to test it.
My only question now is - "How can I make sure I have the correct impedance match to the new 31" external antenna and what other considerations should we have.
What do you think?