Notice the vertical irregularity above the door opening. I call this a stress mark. You will find these in older homes: usually 10-years or more. The cause is fairly simple. Instead of placing an entire sheet of drywall over a door or window opening and then cutting the drywall to reveal the opening, scraps of drywall are used near the top of the opening. When scrap drywall is used, you get joints between the pieces of scrap. Over time there will be some degree of differential movement between pieces of drywall.
What you get is what is shown in the photo above. Stress marks are due to age and what commonly passes for acceptable workmanship.