Usually a throwout bearing will make noise at idle, too. Easy way to check is to slightly disengage the clutch. If the noise changes, then replace the bearing. Otherwise, it's a lot of work best spent elsewhere.
Does the noise occur only when the truck is moving, or when the engine is revved up? If only when moving, look to the drive train. If when revved up, probably in the engine compartment. Speed up the engine and get out the hose. Start with generator, water pump, and listen around.
