Mike

Have you got the exact Yamaha ones with the metal running through them or cheaper version still made by Acerbis? I have seen copy ones that look exactly the same as the genuine Yamaha ones but they too could not fit the handlebar weights. They however did not experience this vibration.

I would say forget the sand in the handlebar trick, ditch the copy hand protectors and get the genuine article. I have genuine ones with the end weights in and have never regretted it or had the problem you have reported. The stock Yamaha bars are not the best but I say get better hand guards.

Cut corners else where but not hand protectors.