This only happens at low speeds. Warm weather makes it show up more, from my experience. Engaging 4H will immediately cause the issue to cease.

I'm fairly confident, through internet searching and finding other owners with the same issue: the problem is the Front Axle Disconnect bushing. It has too much play and causes the Intermediate Drive Shaft to rub, resulting in this horrible noise.

But good luck getting your repair shop to figure it out and/or believe you.