Id say your friend might be right , sounds like a brake shoe problem , it may have cammed over as we call it in the car business, worn out shoe has come lose, and is resting against the rotor, making a rubbing noise let me know ,

Best bet is the brake pads some have wear tabs that make noise to alert you of the problem [squeel] the other problem you said you hit the brakes hard somrtimes the brake piston over extends it self and wont retract generaly with heavely worn pads and the pad is held agains t rotor and makes grinding noise it will over heat rotor and pads the longer you wait the more damage rough guess is pads rotor and wheel caliper dont wait too long the front brakes are compromised

Well i had a similar problem with my 1997 truck, just take off your wheel and look at it cause one of my bolts on the back of the brake caliper had come out and the caliper was sitting on the rotor. but when you press your brakes can you push the pedal all the way to the floor with ease or is it hard?

Try adding differential fluid. drive a couple of days noise should stop.