[wingnut60]

Leaves me at a loss as to where the beep came from. Appears to have corrected itself.
I can't think of any other possible source that you haven't gotten to already.
If it happens again--suggest you get in basement and try to pin down where it is coming from...open all compartments and check while it is beeping?
I don't have a Montana, so don't know the arrangements of the compartments and what could be located where. Hope you figure it out.