Just today my doorbell started ringing by itself and/or buzzing instead of chiming. This is a wired unit using a transformer (I
presume it is in my crawlspace somewhere).

I disconnected the one and only outdoor button and made sure that the 2 wires were not touching each other. Also, the insulation
looks good as far as I can see (which is not much).

The doorbell still rings by itself or buzzes.

I disconnected the 2 wires at the bell unit on the wall and measured 12.4 V AC across them. I also think that there is continuity,
as the I hear an intermittent beeping sound when I switch the meter to continuity mode. I guess it beeps intermittently instead of
a solid sound because it is AC??

When I reconnect the 2 wires to the bell unit on the wall (outdoor wires still disconnected and not touching), I can make the
doorbell ring. If I tighten the screws well, I get a constant buzz.

It seems that somehow I have a closed circuit. There has been no tinkering with wires that might have caused this, unless I have
mice in the crawlspace.

Is this a bell unit, transformer or wire problem? Any suggestions about what I should do next?

Thanks.

Vince