So I just replaced all four pads on my Trek hybrid's cantilever brakes (...for the first time in eleven years, he admits sheepishly).
Recognizing the potential for my own mechanical ineptitude, I then brought the bike into the LBS to have them adjust the brakes: center them, set the spacing, tweak the cable tension, whatever the heck professional wrenches do when an idiot like me brings a bike in and says "Brakes Need Adjusting."
And they did a fine job, inasmuch as the bike stops firmly, assuredly, and decisively. Except the front brake also makes A GODAWFUL CATERWAULING SQUEAL when I use it. I'm talking serious diesel bus/garbage truck kind of brake squealing, a louder, more horrific shreiking than even war-mongering banshees would emit. It's deafening, it's embarassing, and it's relentless. Mostly happens when I'm going down hill and/or coming to a quick stop. Once it starts, no matter how gently I try modulating the brakes, it just keeps going, like a siren. People four blocks away are ducking & covering.
And the back brakes, which are the exact same pad, are perfectly silent.
Any ideas? I beg of you...my ride partners beseech you...my neighbors implore you.