There's a difference between brake squeal from glazed pads and the grinding from over worn pads.

BOBS is correct, if your pads are worn beyond safe use, your sensor will notify you on the dash board. If you replaced the pads without doing the proper procedure of breaking them in, you could have glazed them, which would cause a constant squeak when applied... Kinda sounds like a BUS...

You can fix the squeal by removing the pads and taking some heavy grit sand paper to them and scuff them up quite a bit, then use a very fine grit grinding stone "CAREFULLY" on the surface of your rotors and pads. The stone I use is the same as you would use to hone a knife...

I use Carbon / Kevlar racing pads on my car and they glaze over quite easily and cause some BAD squeaking after a few hard days on the track... This fixes the problem...

Good luck...