Bora WTO rim brake “groaning” noise — toe-in not the issue, what gives?

[dddd]

Originally Posted by hernium

A possible solution might be to try a vibration reducing washer made out of a dampening material - elastomer or neoprene maybe - where the caliper mounting bolt meets the frame/fork.

I would avoid this approach for two reasons, first that the nut may not stay tight for long, and more importantly, that the "hub" of the pivot bolt needs to be rigid against the frame in order to prevent any cyclic bending load being applied to the center bolt itself.

I have an old Cannondale with canti's, and struggled with noisy vibrations for a long time. After much toeing and a couple of pad changes, a third different set of pads finally cured it. I thought it was cursed, especially as the seatstays on that bike look quite rigid.