Clock announcing time when it shouldn't

Years ago, I turned on "announce time on the hour," but when it turned out to be stupid (for US locale, instead of "Ten o'clock" it says "it's ten hours") I turned it off. Three days ago, when I wasn't even near the laptop, it started announcing time again. I knew I hadn't changed it, but I looked and it was still Unchecked. There have been no recent updates to the system to explain the change in behavior. I tried turning it on and back off, but it continues to announce. Before I turned it off again, I also changed "on the hour" to "every quarter hour" but it is still only doing it on the hour (when it shouldn't do it at all). Why? and How to fix? I moved Library/Preferences/com.apple.menuextra.clock.plist to /tmp but that changed nothing (and changing the setting did not recreate it). I opened that file in Xcode, and it contains only two of the eight time preferences.