It's hard to say
to me it sounds like somthing expanding and contracting..... but I'm not there. look closely for any water damage that might indicate a leak. (if you have a crawl space) go underneath and look.
Should you worry about it?
how long have you lived in this house?
I'd suspect it's harmless.... but again I'm not there.
It sounds like it'll drive you crazy before it'll cause damage.
You can open up the wall for the fun of it
look around.
If you find no reason to open the wall don't do it...
Learn to sleep with the radio turned up.
Using a contracter to track the noise may become expensive....
You can investigate it yourself.... but.... well good luck.... This may be a long and frustraiting road to a solution.
dances-with-pumps