i just got my brakes changed and i still hear a loud sound when i hit my breaks. literally sounds like the car is going to fall apart haha like grinding metal. i never had a prob with my car until i went to the shop for the first time to get my breaks changed.  

If the brakes are not working right; take the car back to the shop and tell them you paid to have it fixed correctly. If they don't want to fix it, or give you a bunch of crap that it will cost more money. Tell them you're going to call the California Bureau of Automotive Repair and the Better Business Bureau on their butts. Reputable shops won't have a problem taking the car back and fixing it.

I learned how to fix my own cars, learned alot by just getting some tools and going at it. Now people pay me to fix their cars.

It's possible one of the pads slipped out of place on caliper when they were installed causing a grinding sound. Or they didn't put any anti-squeal on the back of the pads.

Don't wait to go back to the shop, do it immediately. I live in West LA, I can point to a decent shop if you need more help.  

they probably broke the cotter pins and didn't replace them properly so you have play in your pads, dont be driving like this, could warp your rotor and cause brake failure to a overextended caliper piston on the seal, take care of this now, if anything happens such as a wreck, they are liable for your faulty brakes, u take care  

I know this sounds stupid, but it happens alot. Some inexperienced dope might have put the pads on backwards. Also, you didn't specify if the sound was coming from the back or front brakes, or all. And what kind of car is it?