I know this is an old thread but I have been having the same issue with my Rocker. That noise is super loud and annoying, I find myself grabbing the speedo all the time to shut it up. I have tried foam but its still there. Anyone had luck with anything besides ditching the speedo altogether. Call me a ***** but i like to have one...
Remove the dash of the tank.
Remove the tach of the dash and you can will view the screw of the holder of the tach.
The vibrations come from the cup holder of the tach.