Howling

Noisy wheel bearings are a common source of a humming or buzzing noise but that usually doesn't go away at higher speeds. I also ran into a radiator fan motor once that caused a howl above a certain speed due to air flowing through it.

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.