Warped rotor and worn out brake pads.
A grinding noise when braking can occur when the brake pads are going bad. You are hearing the brake grinding on the metal discs.
wheel bearing?
They could, yes.
Possibly the wheel bearing, if it makes a whiring noise when you accel. Or cv-axel, if it sounds like its grinding.
Brakes
Bearings, cv shaft, or brakes.
Brake linings worn? Wheel bearing?
no oil
Certain types of tires may cause a brief humming noise after your initial acceleration. The transmission may also cause a brief humming noise.
i hate answers.com
You need new brakes
I'd try changing tires, worked for me.