might this be the sound of some bad brakes? i'm driving (street/freeway) and sometimes i hear this noise. it happens when i'm driving, not when i apply the brakes. i have a 2000 f150. and i haven't had my brakes check. i'm assuming that's the reason. what the average price for brake repair?

 

Pull the wheels and check the pad thickness. The screech you hear maybe coming from the warning tabs.
I have a '97 F-250 LD and I ahd replaced the front ones around 62K miles and they're due now for replacement at 95K. I also tow a 4000 lbs boat almost every weekend.
I also have 4 wheel disc brakes and the rear pads went first at 52k miles. Why the rears went first is beyond me.

 

if they are newer pads, ensure that all of the shims have been added. These shims ensure that the pads sit in the proper position to meet the rotor.

Cheaper pads don't come with these but apremium pad would.