My truck has developed a clicking sound associated with the drivetrain. It usually happens right at throttle tip-in when gently leaving a stop. The sound is one single click that sounds like a muted cowbell. I've crawled under the truck and shook/pounded on just about everything such as the exhaust and driveshaft, but was unable to duplicate the sound. The truck does have air lift bags on the back, on which I have inflated to 20 psi and tightened the fasteners. Any ideas? 2003 Tundra Access Cab 4WD 4.7 Litre.