If it's a rather high-pitched squeal, that is a common result of using the newer higher-quality linings. It's better material but it is prone to making noise, especially in humid weather. The noise usually subsides when the linings get hot.
There are a lot of things professionals do to reduce and prevent noises. One common trick is to bevel the edges of the new pads to eliminate the "fingernails-on-the-blackboard" screeching. Special high-temperature brake grease is used on all contact points between the pads and calipers and on the caliper mounts. It is extremely important to not get any type of grease on the friction surfaces. That includes fingerprint grease. If there is grease on those surfaces, it must be washed off before the linings go through their first heating cycle. That grease will soak into the porous cast iron rotors and brake linings and never come out. That is a common cause of a squeal. The surface finish on machined rotors is important too. New rotors already have that finish and don't require machining.
If the new linings aren't broken in properly they will become glazed. Braking power will be reduced, you'll have to push harder than normal on the brake pedal, and the pads may chatter or squeal. Most mechanics start the break-in process for you but they usually fail to tell you what to do after that. They will test-drive your vehicle to check for proper operation and noises, and along the way they will perform a few harder than normal stops while giving time for the linings to cool down in between. Those hard stops help the new linings wear down to match the microscopic grooves and irregularities in the rotors' surfaces. Until that is done, braking performance WILL be reduced because the pads aren't making full contact yet, (microscopically). If you just throw new pads on and go out driving like normal, you will have to push harder than normal on the pedal and that will lead to overheating the linings. That will melt some of the binders in the material leading to glazing. Think of that glazing as a thin layer of varnish. As the linings get hotter, they lose their "coefficient of friction" which means they don't grab very well. In response you have to push harder on the pedal and that makes the linings get even hotter. Eventually no matter how hard you push, the vehicle just keeps on going. At that point the remedy is to let it sit for a few hours so the linings can cool down, then go out and drive it like normal. The pads will be fine once they cool down. All of this can be avoided by simply going easy on the brakes for the first 100 miles. Some shops even have information tags they hang from the rear view mirror that spell out the break-in procedure.
That is more of a problem for people who pick up their car from the repair shop, then do a lot of city driving right away. That is what really gets brakes hot. People who drive to the country, on highways, or for short distances don't develop much heat in the brakes so that brake fade and the potential for glazing isn't a problem.
Sunday, June 3rd, 2012 AT 4:29 AM