At first we suspected the need to just add or replace some shims in the valve lifters, a simple fix. After further investigation, we suspected worse and cut open the oil filter to check the oil. There was a significant amount of aluminum (non-metallic) shavings stuck to the paper in the filter. Bad bad bad.
|Inspecting the paper filter inside the oil filter. Bottom left of the photo you can just see the inside of the metal canister it came from.