1996 Ford F-150 My truck started squealing recently.

Need a lot more to go on. Is the noise coming from the front, rear, middle? Does it change pitch with changes in engine speed, road speed? Does the sound change when you turn as in changing lanes left or right?

There is a tool you might be able to borrow or rent from an auto parts store that borrows them called the "Chassis Ear". It is a set of six microphones, a switch box, and headphones. You clip the microphones to suspect points, then drive around while listening with the headphones. You can move the microphones around to zero in on the source of the noise. Be aware that many mechanics have never seen or even heard of this tool. Suspension and alignment mechanics use it to find rattles, squeaks, and other noises.

The only thing I've ever run into that didn't change pitch was an electric radiator fan motor with bad bearings. The howl wouldn't start until about 45 mph but it had to be really cold. I could never make it act up in the shop because it was a lot warmer in there. Each time I went outside on a test drive I had to go about five miles before it got cold enough to howl again. The air flow while driving made the fan spin and the noise would stop by about 20 mph. I don't remember how I found it but it was by accident. I tied the fan to prevent it from spinning, then there was no more noise.