The conditions under which it happens based on your description, leads me to believe it is pinging. But, I wouldn't describe that as 'clickity-clack.' If it is pinging, try some higher octane gas to see if it goes away or run a decarb through the intake. BG 44k is a good chemical to run in your tank from time to time.
If pinging isn't your issue, post a video of the noise you're hearing if you are able to.
Zone 4,32s,Herculined,roofrack,Zeon 8s,grill guard,washer relocated,DIY tire carrier,sliders.
Also sounds somewhat like the driver's side exhaust manifold bolts snapped.
Get under the hood when cold, engine running. Tug on the throttle cable under the airbox to rev the engine a little and if you hear it from the driver's side, by the heat shield, Bob's your uncle.
Common issue and plenty of threads on the topic.
2000 Laredo 4.7L Selec-Trac. 177K miles, Leather, 245 tires, tow package, crappy CD changer, full size spare, roof cross-rails & sunroof. Changes & fixes: Rear Addco sway bar & greasble bushings, upgraded headlights, upgraded tail lights, new hood struts (replaced 2X), new rear hatchglass struts, new radiator (replaced 3X), new oil pressure sending unit (replaced 4X), 2 new speed sensors, 2 new door lock actuators, new ignition key cylinder, chrome front tow hooks, Mobil 1 Synthetic 5/30, Purolator Pure One oil filter, EBC slotted & dimpled rotors, EBC Greenstuff pads, new front shocks (replaced 3X), new rear shocks (replaced 2X), new IRO steering stabilizer, new timing chain cover, new water pump, thermostat, new thermostat housing, new high pressure power steering hose, Michelin-X radials, new sunroof assembly, new single-piece lug nuts, new exhaust manifold studs & gasket on driver's side, new Durango alternator. Jeepforum.com sticker, Visit cobaltboatsforum.com when you can!