This is a common problem caused by a home “settling in” or drying wall studs. The best way to fix it is to take a nail set and drive the problem nail on into the stud. Then, just above or below the pop, install a drywall screw to hold that area of sheetrock to the stud. Then, spackle the area, sand and repaint.
Always keep the various paint colors in your home somewhere close by. It only takes a little sample for modern stores to match it almost perfectly.