Spring rains, basement is getting more humidity and moisture. Install a dehumidifier and use it. If possible, set it up so that it can drain into a drain in the basement floor. If you dont have a drain, then, you will have to check it a couple times a day and empty it.

Thanks, I just put one in there. Will see if it works. I’m ok with opening the walls if there’s a way to stop it from happening again.

Condensation causes risk of mold and mustiness within furred out walls against concrete. I assume the other 2 walls are finished in front of the concrete.

That seasonal period is probably between use of heat or a/c, so there is not a lot of air movement, and temperature/dewpoint conditions are ripe and the mustiness is carried throughout the basement and probably somewhat upstairs from stack effect.