Motorola Droid :: Sometimes Rings Only Once For Incoming Call / What's Going On?

Often my Droid will only ring one time for an incoming call. If the call is left unanswered it is auto-answered after a "normal" amount of time. But I can watch the screen of my quiet Droid after the initial ring and count the seconds until it's auto-answered with my recorded greeting. It should be ringing during that time.
It seems to do this randomly, though it's really tough to troubleshoot and tell definitively. I sat for two hours with my wife's Droid, my laptop phone program and our regular house phone and got consistently inconsistent results!
I've yanked every phone call specific app and reinstalled them systematically, rebooting each time. I've taken a look at system apps to see if there is a conflict. I've also looked at (and pulled & reinstalled) audio setting apps looking for a conflict.
I've changed ring tones to MP3 clips, and while they do play in their entirety, they usually repeat and they are not. I've even done a hack to the system/build.prop file that changes the delay before the phone rings.
I just can't seem to figure out what's going on. Anyone have any ideas?