2004 Toyota Tacoma Front whistling noise during idle

After a long road trip involving some 4-wheeling, I noticed my truck is making a whistling or high-pitched reeeee sound kind of like a really quiet dentist drill. It comes on about 15 seconds after I turn the truck on, is a steady high pitch at idle, drops down in pitch and then goes quiet when I accelerate, comes back when I'm coasting, and then stops initially when I brake and then starts, going up in pitch til its high pitch. The whistle happens whether I'm in any gear including neutral and whether or not I'm in 4wd. I can hear it as clearly inside the cab as I can outside the cab with the hood up, and it seems to be coming from the round transmission hub. Any specific ideas on the repair involved? I'm trying to decide whether I should attempt a fix myself or take it into a mechanic.