Try the easy fix first, go to your local parts store and get a couple of packages of caliper glue, lube or what ever they call it, I forget. It's basically a glue like substance that comes in a tear open package like ketchup, it cushions the pad from metal to metal contact from the caliper. Spread it on the backside of each pad and let it dry, reinstall the pads and that should take care of your noise, I'm surprised your mechanic didn't do this for you!