the prior owner's xm radio subscription ran out today, and, for the first time, because we weren't going to use it anymore, we turned off the xm radio receiver. the normal radio reception magically returned. when i realized this, i turned on the xm radio to test, and the radio reception vanished. good thing i figured it out fast, cause with the loss of xm radio stations, i was starting to think i might re-subscribe. now, i can listen to my favorite jazz station, etc... thanks to everyone who had suggested possible causes, i got lucky before i started taking things apart!