My friend says rod bering noise is often mistaken for valve noise and I thought I have valve noise but I hear it better when I go under my car with it started!!! Its got 156k miles on her
rod bearing noises will change with load, whereas valve train typically will not. with the car idling, unplug one injector at a time to see if the noise changes. the noise should just about dissapear if it is rod bearings or piston slap.
