WARNING: This page is about a different car, the 2004 Mercury Mountaineer and 2004 Ford Explorer. However, it is still accessible from the selected car via links, so may be relevant.
Inspect the hydraulic valve tappet and roller for damage. If any damage is found, inspect the camshaft lobes and valves for damage.
Fig 1: Inspecting Hydraulic Valve Tappet And Roller For Damage