Crack where wall joins ceiling
Our kitchen has a vaulted ceiling. At the high end, a crack has formed where the wall joins the ceiling. It started small and gradually got wider. I can't say how wide it is because it's very high up and I cannot reach it, but would guess it's about 1/4 inch in places. Possible causes: (1) settling of the house, which was built in 1985; (2) when we bought the house in 1991 we had the popcorn ceilings made smooth before we moved in, and this may have disturbed some sealers at the joint, if there were any; (3) inadequate or no insulation above the joint which produced larger than normal changes in temperature with the seasons (central North Carolina), and caused an instability in the joint.
Have I diagnosed the problem right? How do I go about getting it fixed (by a contractor, not DIY) before we have the kitchen painted so that the problem does not recur?