Recently I got a new bike (new frame to be exact), and swapped over all of my parts to the new frame, including the wheels (aluminum rims, standard brake pads). The only change is the brakes on the new bike are the direct-mount kind (Bontrager Speed Stop, if it matters), which I had no familiarity with, prior to owning this bike. Recently, I have noticed that my brakes start to squeal during sustained braking, generally on high speed descents, and usually only after a few minutes of descending. This leads me to believe it's a heating issue, but I don't know for sure. This didn't happen with the same wheels (and pads) on my old bike, descending the same routes, so I'm at a bit of a loss as to why this would happen now.

Does anyone have any experience with direct mount brakes, as it relates to brake squeal, and different kinds of rims? Could it simply be a toe-in issue? Something else? I'm definitely going to ask the shop that built up my bike, but I thought I'd throw it out here too.