Brake Noise

I have a 2001 Chevy S-10 Xtreme and am having a huge problem with brake noise. At 32,000 miles, I went to a Firestone dealer and had my front pads replaced with their top of the line semi-metallic pads, had the rotors turned and bearings repacked. Afterwards, I started hearing this deep grinding noise like something was digging into the metal. I went back 2 or 3 times and they said everything was okay. Over time, my truck has been having issues with a vibration when hitting the brakes, so I took it to Pep Boys (41,000 miles on the truck now). I had them replace the rotors with factory parts that I bought at the local Chevy dealership ($140 a piece) and had them install ceramic brake pads. They said the front pads and the rear shoes were not in need of replacement, but the rotors were warped a bit and there was no meat left to shave off. They replaced the pads and rotors, cleaned and calibrated the rears, and all was great or a day.... Now I am hearing this noise again and it is driving me nuts.
Does anyone have any ideas of what might be causing this issue? Siezed caliper? Bad bearings? I have always used standard pads and shoes costing $40-60 on my vehicles, and always replace the rotors with aftermarket products but this time I figured I would go all out and get top of the line products. If this is top of the line, I'm going back to the cheap stuff!!!

This is strange...so is the noise constant or only when you apply the breaks? If constant check the dust shield, if not that maybe go see if you need to reaplce your hardware for holding your pads in place. If there is no hardware for that, think about putting some break silicon on the back of each pad this helps reduce noise and or shuddering. Give some more detail on the noise when it happens and such...

The noise only happens when applying the brakes, and usually at low speeds (5-15 mph) or if I do 30-40 and lay on the pedal to stop quickly.

It rained here last night, and on my way home from work I was listening for the noise so I could take it back to PepBoys, and it was still there but not nearly as loud.

I'm going to take it back to them today to see if they can fix it, otherwise I will try the silicon option.

does it make the noise the whole time holding the brakes or just when you initialy applying them?

May sound really silly but if the brakes are checking out ok, have you checked your universal joints...believe it or not they can make the exact noise you are describing...

I may be wrong on this, but I believe that you cannot repack the bearings on the front of your vehicle. Hope you didn't pay too much.