[Auf los!]

I resolved the mysterious single beep when locking/alarming the car. It is not well-described (at least not that I have seen), but part of the anti-theft CDR220 system is a piece of vinyl glued into a depression in the side of the radio chassis. This insulates the chassis from the tab that sticks out of the frame. This seems counter-intuitive to me. You would think the system WANTS metal-to-metal contact, and if it doesn't get it, there's no radio, it must have been stolen. But it's the other way around. No contact means everything's hunky-dory.

Anyway, on my radio, I have pulled it out and stuck it back in so many times that this little piece of vinyl was peeling up...it's been almost 20 years, after all. It was peeled-up in such a way that it was allowing contact between the tab and the chassis. So I just pulled the connector of the anti-theft wire off the frame, put a piece of electrical tape over it, and no more "somebody's stolen your radio" beep or alarm going off for seemingly no reason.