I searched here and found one reference to this problem in 2004, but no solution.
A few days ago, I had my radio on FM and I turned on the rear defroster. The radio changed to mostly static. Defroster off, static off. Very repeatable. I have since, tried it in several other locations and times, and the same thing happens.

Has anyone else had this happen, and more importantly, is there a fix?

There is a splitter module in the rear pillar.....driver side....that the radio antenna and defroster both hook into. When one or both sides begin to corrode they interfere with one another. The solution here would to replace the splitter module with a new one and you will be good to go.

I know this because my father-in-law has a 1999 Buick Park Ave that shares a lot of modules that the 2000+ Bonneville'* have. He had the same problem and we found out that his splitter module was all corroded inside. Replaced it and problem fixed!

Interesting... I'll have to take a look and get back to you.