There is a Service News and Techline summary to improve AM reception. It is *not* a TSB. My previous dealer (Concord Acura, which sucked) denied its existence.
My new dealer (Pleasanton Acura, which is good) specifically mentioned it and then printed it out for me. It has to do with cleaning connections on the antenna base, or replacing the antenna assembly (both require pulling down the rear of the headliner).
It made a world of difference.
The inital reference is in the Feb04 issue of ServiceNews; I don't know the date of the subsequent techline summary.