I do not know what is going on. It seems to only happen at night. One time
it happened at 3PM and its getting worse. Its not happening about every 3-10
minutes. There is a loud high pitched screech that seems to come from the
wall near my bathroom. its hard to tell.

i thought it was the pipes so i turned off the main water valve and this did
not improve anything. I do not know why it doesn't happen during the day.
The screech lasts about 1 second, but recurs.

any idea?