Strange intermittent popping sound from floorboards
Like Kris said it's most likely:
Expansion and contraction due to fluctuating   temperatures and humidity levels.
There are several options to address this:
If you own the house, and want &quot;a squeek free floor&quot; hire it out to a local handyman.
Otherwise you will play chase the squeek for weeks with a mix of screws, nails, glue and braces.
If you don't own the property, call the owner.