I've been trying to find this annoying squeak for awhile now. I yesterday jacked up all 4 corners and put it in 4 wheel drive and drove and it would BARELY do it. It starts after I drive for a few minutes. Front left wheel is where I think it's coming from. It doesn't change when brakes applied it increases with speed and it sounds like just one squeak not a long squeal. Ujoints look like they've been replaced. Doesn't matter if the hubs are locked in or out it still does it. Any ideas? 1996 f150 5 speed 4*4 4.9L 201,000 very rusty

 

Sounds like possible sticking caliper. Add in the tiniest amount of imperfection in the rotor and you get a squeak ..squeak...squeak. Could be it.

 

rotors are warped. but it doesn't really change when I apply brakes. Real head scratcher

 

brake pads were locked in place. lots of rust build up under the hardware. Took my angle grinder to it now no more squeaks.