rear discs suddenly noisy

[6spdYJ]

My rear discs have started braying like a mule under light pressure. When I give it more pedal they get quiet, but stop way sooner than I want to. They stop fine, but just sound obnoxious. I've been running them for about a year and a half. They have lots of pad left - nowhere near the tattle tales. Even wear on the pads and the rotors also look good. Pads, pressure, contamination?

[6spdYJ]

Rusted caliper slider stud.

[Tumbleweed13]

Maybe the caliper is a little loose.

Dirt, been in the mud lately?