I think the first thing I'm going to do is drain the engine oil and check for any metal, it seems to be a odd one, under engine braking the noise completely disappears as soon as the throttle is pressed it's back, it sounds bad enough to be big end failure but the engine has oil pressure and starts ok.
It's not a constant nocking but more like something has come loose, I have a thought it could be the wet clutch or the one way bearing.
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