WARNING: This page is about a different car, the 2007 Lincoln Mark LT and 2007 Ford Pickup. 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: Identifying Hydraulic Valve Tapped And Roller - Push Rod Engines