yep-it is either at the top _where the strings connect
or in the middle...the bridge is held by tension from
the skin head...perhaps the skin is natural fiber (animal
skin) and is weather-sensitive. They do make synthetic
ones which would not be as tempermemtal.
by the way, banjos always make that
"incesant blink blink bong bong bong bling sounds "
whether in tune or not.