The door is noisy going up or down, louder than it used to be, with a grinding or popping sound near the top of the travel. Or it moves unevenly, one side dropping faster than the other, which usually points to a spring that's lost tension or a cable that's starting to fray. On older installs from the early 90s, you might also see the opener struggling - reversing partway through a close, or taking two or three tries to get going, which is a motor or logic board wearing out rather than anything wrong with the door itself. Rollers that have gone from nylon to metal-on-metal grinding are common once a door's original hardware hits this age. None of these are emergencies on day one, but they don't fix themselves either, and a spring that's close to failing tends to go all at once, usually while the door's halfway open.