Thanks!
Big thanks to TheWorm! I finally got around to getting my AM reception taken care of. When I described the problem over the phone to the service advisor you could just tell he was starting to blow me off until I gave him the details from your post.
Just got the MDX back today, they tried everything mentioned in that Techline summary and ended up doing a "Goodwill" replacement of the antenna. Huge improvement.
This place is great!