You can add some rubber hose over the mounting studs to hold the speedo tight in its mount. The rattle is just the speedo moving.

Others found a quicker, easier way. I used a piece of self adhesive black foam rubber from a window unit air conditioner, pulled the speedo, laid it on the tank, with the paper still on, got the speedo outline, cut , placed, Tedious,, and that fixed it. But, for all I know, just me messing with the springs is what did it.

Almost forgot. What's the headlight mod? That dam thing squeaks and rattles also. More rtv?