What can cause a toyota 4runner to have high pitched noise?

Unidentified noises are always fun, aren't they Unfortunately, there's no single thing that I can tell You that could be causing that high pitched noise on Your Toyota 4Runner. For example, if it's a sort of screeching sound, that's maybe going to be Your serpentine belt. If it's more like a constant whining sound, it could be what's known as "alternator whine", and usually You'll hear this as though it's coming through the radio. Something else it can be, and obviously, if You hear it in this context, is the brakes: If something is touching the rotors, even a little bit (like, not kidding, the dry stem of a leaf!) You'll hear a very shrill sound. I'd say the first thing here is to check all Your fluids, and visually inspect all Your brakes and belts for obstructions.