Easy check of the valve train.
Warm up engine. Remove valve cover. Put some rag around the engine to collect the oil. Wear gloves.
Start the engine, idling, put your finger on each rocker. If the sound changes you have found the culprit.
Excellent suggestion, I'll give this a whirl. I have quite the chore list going, it's a good thing I have the next few days off to work on this. Updates coming after I go get greasy for a while.
