Light clicking sound while in motion

[R.Smith]

If it's governed by speed then it's reacting to the gravity in the way a roulette ball hangs to the rim of the roulette wheel until it slows enough to fall free.

I had this problem but it had nothing to do with the wheel or brakes. I have aluminum wheels with a wide inner lip so the guy who balanced the wheels put "sticky weights" inside the rim instead of the clip on type. The weights were grazing the disc break assembly and, because they were lead, it went "chunk chunk chunk" instead of sounding metallic.

[idaford]

Ive had problems with a brake part falling off and it made a slight ticking sound when I drove slow. It was in the right rear of mine. A matter of fact I heard it again just the other day. I guess I need to tear into it again. I really hate 3/4 ton rear ends.
So if it were me I would jack up your truck and check your brake hardware.