Originally Posted by
digger
I say that because when I first started using discs 6 years ago, I would routinely use rubbing alcohol to clean the rotor on the BB5s (my OCD). I had squealing issues like you wouldn't believe.
Oh, I believe it. If I clean the rotors with rubbing alcohol, I follow that by cleaning them with Clean Streak. It's a nasty chemical, but it's far less likely to leave the rotors squeaky/moany.
He thinks that the grit picked up when off-road cycling keeps the pads and rotors from becoming too smooth, you know that shiney look you get on brake pads (?), that is what he means and he feels that this is the cause of most of the squeal.
I've occasionally fixed brake squeal by grabbing handfuls of dry dust and rubbing it on the rotors, then riding while dragging the brakes, so I can believe that one too
In the bigger picture, some brake squeal will be transitory, some is caused by wetness, and some is because disc is disc... you're putting substantial force on a thin rotor with a caliper attached to a semi-rigid mount, and stuff IS likely to flex, harmonize and vibrate in some circumstances. Expect at least occasional noise if you go that route.