I have a pair of Hayes HFX9 hydraulic brakes and experience the same deafening squeal. It happens “all the time”, whether the conditions are dry or wet. I’ve used alcohol to clean the disc and the pads which seem to eliminate the problem for about two miles worth of riding but then it’s back to the squeal. It’s gotten to the point where it actually vibrates the bike while braking. The problem continues despite changing the pads every 700 miles or so. I’ve had the brakes serviced at a few bike shops to no avail. Would I be throwing my money away by replacing the disc as well as the pads? I’m realizing it’s hard to find a definitive answer to this problem. Any additional advice appreciated.