Brake Question, need help

So I noticed a while ago, that when i first start my car and come to a brief stop (before driving more then 50 ft at an accelerated distance) there is a terrible skreaching noise. However, after I drive for even 30 seconds over 30 miles per hour and then come to a stop, there is no noise. And there is no noise at every stop during a whole drive. What is wrong? I know its not my front brakes because I recently had them change, along with rotors and calipers in front. I have never had my back breaks changed, mainly because "firestone" has never told me i needed to. My car is 3 and 1/2 yrs old. Any comments welcome. Thanks

aftermarket brake pads... probably those "long life" pads they sold you are source of your noise

its not uncommon for rear brake drums to get a bit of brake dust build up and make noises when you first start apply the brakes in the morning...assuming this car has drums

It very well could be the front brakes though. Brake squeaking/squealing from the front is a very common issue, even on brand new brakes.

First you need to figure out if its front or rear. Roll down your windows and apply the brakes as you're driving by parked cars, the sound will echo off the cars and make it obvious if its front or rear.

DONT WORRY MAN! There's no need for concern. Alot of cars do that on startup. That's generally because rotors develop surface rust over night. Sometimes, it's just because the salt or dirt from the road deposited on your rotors. So don't worry about it.

If your breaks are squeaking all the time, then it's because you either have worn out pads (which might be the case for the rear pads) or it's because they're low quality pads without the noise reduction back plates. SOMETIMES, when you get your breaks changed, the mechanic doesn't clean the calipers with break dust remover and that might cause your pads to squeak all the time.

Its not the fact that Im worried about it, its just a sort of embarassing thing that I want to take care of. After tailgating at the Sabres/Penguins outdoor game last week, leaving the parking lot was bumper to bumper and there was screeching the whole way out of the parking lot until we got out. What can be done to rememdy the problem (what should i suggest to have done) if i take it into a mechanic? Thanks guys.

good information guys. this message is for mazda tech. you were saying that sometimes people are sold "long life brakes". i was into the mechanic not too long ago and i was told about a set of brakes whcih were exactly that, "long life brakes". The exact name of them was nrs equipped brake pads. do you know anyhting about them? The mechanic said they were worthy of a try. But i dont know this mecahnic and i am not a frequent customer.
Thanks,
Freaky