Unsurprisingly with the mileage approaching 100k the two screws securing the bezel seem to have come loose allowing the plate to move in sympathy with the revs.
Is it just a matter of careful prising off of the glass and its surround to get access? Or, is that a non-starter, and I should just live with it until it self destructs?
Someone is going to ask, may just as well be me.
What bike and year is it?
Guessing it’s this? 1979 V1000 G5
That’s the one 
The outer bezel is usually crimped onto the speedo body. If I’m right, the G5 has an unusual large speedo? Maybe?
You could try prising it off, but they rarely go back on neatly from what I have seen. I guess it depends on how fussy you are about appearance.
I’m no expert but I think it’s the unusually small Rev counter that makes the normal size speedo look bigger.
Thanks for your input. The whole bike looks a little tatty as it’s paintwork is original complete with rust and scratches, but that’s a part of its charm to me. I’ll probably leave well alone until it completely comes apart.