A while ago I noticed that my rear brake had started to squeal when rolling bike backwards. I hoped than after I changed pads and cleaned calipers a few weeks ago that it would stop, but it didn’t. Last ride I did some testing by avoiding use of back brake for a few minutes and found rear brake disk was slightly warm, just a bit above blood temperature, so I guess it is rubbing very slightly.
Anyway, today I decided to have caliper off again and give the caliper sliders a good clean and grease (I didn’t on last pad change). I also confirmed that the piston operated smoothly and that it relaxed open slightly after operating. The EBC pads are painted, which almost immediately starts flaking off unevenly, so I scraped clean the parts that get pressure applied and made sure things were flat and smooth. Finally I chamfered trailing edge of pads.
Went for a test ride and for now pads don’t squeal any more when rolling bike backwards but disk still gets mildly warm when riding. I did notice when working on brakes that the concertinaed rubber boots on the loosely fitting sliders have enough force to keep the caliper sitting with the inside pad touch the disc, so I guess that’s enough force to keep disk a little warm from friction and is normal.