Have you run the engine with the valve cover removed?
That would allow a visual evaluation of moving parts/pieces at least on the top end to eliminate if any of those components are the noise makers.
Not quite understanding what you mean by "Little knocking noise travels with acceleration."???
Any which way, that sound is unlikely to cure itself and internal inspection is probably going to be needed to find it before you can correct it.
Just my $.02 worth.
Dan
