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is it like a screeching metal on metal sound?

 

Could be that the spindle nut needs to be tightened.. that is often the cause and there is a TSB for increased torque.

 

I'd have a double check on the brake pads. The metal "squealer" on the pad makes lots of noise whet it hits the rotor.

The inside pad has the squealer, and tends to wear faster than the outside pad. I've seen plenty of people miss the pads being worn.

 

It is a high pitch metal on metal squeel.

I can check the pads, but wouldn't it only make that noise if the brakes are being applied?

 

Not always, It depends how far the pads are worn. When the squealers 1st start to touch, you'll hear them without the brake pushed, the noise will go away when you push the brake. As the pad wears even more, they will squeal all the time.

Sometimes on rear pads you'll start to hear the squealer in a high speed turn, as the pad shifts in the caliper.