I had problems with my non-factory radio picking up AM properly. The expert at my Smart Center got me wired back in properly so the AM came in great.
There's an AM amplifier that's been replaced under warranty for a few smarts - part # 81623800 - that has cleared up the static for those factory radios. I think it's this external part which wasn't initially powered properly attached to my aftermarket radio. In the threads that I've found, meaux61 seems to be the first that brought up the solution for the amplifier troubles.
If you call your distant Smart Center, you might be able to figure out some options that could work for you.