Walls and Ceilings - Drywall bulging horizontally

Just read through this area and got some great tips on how to fix all my nail pops. I am redecorating my finished basement, and have an additional problem with most of the walls.

They not only have vertical nail pops in many places, but the wall bulges out horizontally about half way up the wall, and also vertically in some places.

I'm certain that this is where two pieces of drywall board butt together. My house is about 20 years old, and the basement walls are 6 feet underground, with 2 feet above ground (ie, small windows at top of wall).

I don't have any water damage or leakage that is visible, and I am using a dehumidifier during the summer. Any help for remedy/repair for this would be great.

"MomRemodeling in Canada"

Use a magnetic stud finder to locate the wall studs, and pull the sheetrock back in flush with drywall screws.
Mud them, lightly sand, and repaint the walls.
Good Luck!