My house makes different sounds in the winter than in the summer as
well, one door doesn't close fully in the winter, and another will
swing closed (not latched) in the winter, but not in the summer. I
wouldn't worry about it, especially if it seems to happen around
consistent times and/or temps.

The only other thing I can say is now is about the time that things
that normally live outside start looking for a warmer place to hang
out.... as long as you don't find any mice droppings you are probably
OK.