bit hard to tell not knowing where abouts on the engine the sound is coming from, but CFB seems likely, as mine sounded simular where I hadn't punch the pins enough to stop then drifting out.
or theres a loose nut and boucing around on the head :lol:
I have asked 'her' to take the rocker covers off and listen to the noise while viewing.....sometimes the noise and what you see coincide and you have learnt something.