I just bought a 2004 F150 4x4 FX4 Supercrew. The front drivers side brake makes a metal to metal type squeeling sound when warmed up (ie after driving for a while). Not real loud but I can hear the sound reflected back at me when driving slowly in tight quarters. Still does it when in neutral (coasting), still does it when in 4 high, goes away when I stop, goes away when I touch the brakes, does not do it when the thing is cold. I took the thing to a mechanic who put it up on lift and inspected the entire underside of the truck. Said all looks great - brakes in fact are new and the noise is probably just semi metalic seating. A few hundred miles later it persists and since it goes away when I actually apply the brakes - I question his conclusion. I am going to pull the wheel this weekend and look. I think there is a shield down there - could that be rubbing a little only when warm?

 

also - the squeeking speeds up when the truck does and vicea versa.

 

Wheel bearing maybe? I've bought some disc brake anti squeak before. It was an orange goo that you smear on the rotor.

 

Your backing plate would most likely make a noise all the time and it would be pretty loud. Sounds like there is a piece of brake hardware slightly rubbing the rotor. When you pull it apart look at all the hardware to make sure there is enough clearance between the rotor and piece of hardware.

While apart you should grease all parts where there is metal to metal contact especially the slider pins and spray the pad backing plates with some disc quiet.

 

Thanks guys.