Carol, John2000 is right on but there may be one other explaination. Is this happening on an outside wall? If so, you could be getting a little water leakage down through the roof from ice damming. Now you have 2 places to look. Check in the basement or crawl space to see if there are any signs of movement of the foundation like cracking walls or joists sagging. Check the attic above the wall for any signs of water. Water can run quite a bit from a leak location but it leaves some indication like a slight mineral deposit sometimes or a damp mark on the wood. Drywall tape breaking away for no reason is unusual. Another cause might be something like putting a waterbed over this wall on an upper floor. If you fix the wall without fixing the problem, it will just occur again.