Original hardware generation
That's often a roller losing its bearing, which on a door this age is frequently the original hardware from a build era (1972-2005) that didn't spec nylon rollers as standard. The second sign is a door that feels heavier to lift by hand than it used to. That's spring fatigue, and in a cold-moderate climate it tends to show up first in the cold months, when the steel is slightly contracted and the balance that felt fine in July suddenly doesn't in January.

