I have noticed alot of riders having complaints about disc brake squeel so I decided to post this. First thing to check is if the calipers and discs are aligned properly, then make sure the disc is not contaminated(brake fluid, greese, etc.). Check to see if the disc is warped which could happen from excessive heat(most likely). Then comes pad material, some brakes have metal or sintered pads which will tend to make more noise then pads that have no metal in them. There are aftermarket companies that sell pads of diff. material depending on the type of riding you plan to do. Lastly, some pads will make more noise until they are broken in others will always make noise. Hopefully this info helps.
Slainte
Matt