Sound like nails being pulled from wood in walls at night
The sound happens night and day (not really mornings) but mostly at night. It started in early summer. When the noise is particularly loud I think I hear squeaking as well but it's hard to say. It sounds like a nail being pulled out of wood that does NOT want to let go. Chewing/grinding sounds too. The sound is in the upper NW corner of my bedroom. I went up in the attic and looked for droppings or any signs or smells of rodent and nothing. There are holes in the screens of the attic vents but nothing much besides undisturbed dust in the corner above the bedroom. No holes on the exterior either that I can see. I am STUMPED. My house was built in 1928 and the walls are lathe & plaster. I'm about ready to pull the walls out to figure out what's going on, insulate that room and just drywall it!
Any ideas would be great!
Flying squirrels could be the invader that you are hearing. These small, quite cute appearing little creatures can cause the sounds that you are hearing. They can make holes in the screens of the window's framing, and will squeeze through an opening in that framing; if necessary chew to widen the opening. Often, a woodpecker hole becomes an attraction to these flying(really gliding)squirrels. They are able to cling to wooden surfaces and chew to enlarge an opening.
I have found these small squirrels had squeezed through large separations between to joining roof surfaces at the valley where they meet.
Trapping may be the answer here. We exclude these critters by a proprietary method; however, it is not practical to describe our technique since the installation is custom installed, and cannot be easily be built by a layman. The squirrels can be removed via live trapping; however, please contact your State's Forestry Department for special instructions.
Other squirrels can also be your visitors; however, the nocturnal aspect of your description seems to exclude them, since they are active indoors until around 8 PM at the latest, and again active at around 6 in the morning. The fliers are busy at late hours. Their peek activity, coming and going seems to be around 1 AM; in my experience.
I hope to have been helpful.