Hi, Tom and Connie. The nails used to attach the drywall to the joists are popping out. It would be almost impossible to determine the cause but the fix is easy. Determine which way the joists run. Using a drill with a #2 Phillips bit, put in 1-5/8" drywall screws a couple of inches on either side of the popped nail along the joist. If the screw goes in very easily, you could have missed the joist or they run the other way--remove the screw not hitting anything. You want to run the screw down to where it dimples the surface of the drywall but not far enough to go thru the paper on its face--be gentle when you are close to having it all the way in. Then spackle, sand smooth and spot paint the spackling plaster. That's all there is to it. Connie, this is easy enough for you to do. Surprise Tom.