Brake squeal is actually the pads vibrating. Often, pads come with a little packet of "goo" to smear on the back of 'em, but I have also heard of people applying a very thin layer of silicone, and even using cheapo rattle-can enamel paint sprayed on the back. I use something like "Disk Brake Quiet" (I think that's right) by Permatex. I have never had to use it on a motorcycle but that was the only stuff I found that would keep new pads from squealing on our '80 BMW 320i years ago... A couple heavy coats, let dry, install/reinstall pads, and no squeal!