That is a high frequency resonance and not engine related. Sounds like something thin and metallic to me? Screen, clocks, headlamp cowling and its subframe are notorious for resonance. Maybe bash plate? Have you an aluminium radiator guard fitted? I know you've checked the screws in the heat shield, but could be a loose exhaust clip/clamp or heat shield itself? Cable routing under the tank?

You going to have to get another pair of ears and hands to help you listen and feel around to isolate what it is. However, the good thing it's not terminal, just annoying!

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