Some of the Hornet guys on the US Hornet forum have reported the same sort of thing. The ways of fixing the problem are many and varied, some change to Renthals and this seems to change the resonant frequency of the bars. Some fill their bars with various expanding foam pressure-can stuff, some change the bar ends, some change the grips (some do them all). Eventually they get to a point where they have abated enough for them to live with

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May be an idea to try some of them, starting with the cheaper options

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This may sound like a stupid question (so please forgive me) but have you considered different gloves? My winter gloves with padding in the palms are really comfy and you can hardly feel any vibes at all, so I'm wondering if you can get gel-palmed ones for summer.
Mick