Could just be bedding. Try finding a nice, quiet, flat road. Get upto about 20mph and jam the brakes on. *Important Bit* Don't fall off! Do this 2 or 3 times, then: Change into a gear you can push easily against a resistance (think a hill climbing gear) and pull the brakes on a little, just so they are binding. Ride the bike, like this, for 500M or so. All should be good. I do this each time I have changed pads (or, more irritatingly, after I have washed the bike). I removes judder and squeeeeeel