Why has one of my controllers become very noisy?

I’ve got a pair of DualSense controllers — version 1, I think. Both white, one two years old, the other a year and a half. I’ve lost track of which is older.

One of them has become very noisy whenever haptics are engaged, with frequent buzzing sounds. The other controller, playing the same game with the same settings, is as quiet as it ever was (which is to say, not silent, but not buzzing so loudly that it’s constantly noticeable).

Any ideas or suggestions to quiet the noisy one down again, short of replacing it?