Could be the clutch fork....assumed it was lubed properly before installation. Could be the transmission input shaft housing having excessive clearance that the throwout bearing race rides on, or the wrong input shaft housing length the transmission has for your truck. Assumed all that was checked by the installer, or whoever rebuilt the transmission that belongs in your truck. Could even be something else totally unrelated when you load the clutch, something else stops making noise like a loose shield rubbing on something.