[fignon's barber]

I had this squealing issue on my Orbea Terra with Ultegra disc about a year and a half ago. Tried cleaning/pads, etc. Drove me crazy. After much time on my workstand, I found the problem: every time I applied the brake, a tiny puff of hydro oil escaped from around the bleed screw on the caliper. I called a friend who was a shimano rep at the time. He said it was not uncommon and had me take it to the LBS and had the caliper replaced within a week under warranty. It's worked flawlessly since.