I understand that it could be all of the issues mentioned above but I found out first hand it doesn't take a lot to destroy the valley pan. This picture of the valley pan I just removed. Yes that is a hole(crack). This was all due to my breather caps being to close to the valve cover baffle. They seemed ok but they were not. The engine was and still is running great. This has nothing to do with the pinging but swollen valley pan does not necessarily mean big problem.