WARNING: This page is about a different car, the 2004 Lincoln Navigator and 2004 Ford Expedition. However, it is still accessible from the selected car via links, so may be relevant.
Inspect the roller follower for flat spots or scoring. If any damage is found, inspect the camshaft lobes and hydraulic lash adjuster for damage.
Fig 1: Identifying Roller Follower For Flat Spots Or Scoring