Need a little help figuring out a sound

[heneste]

Mine has some of the floor board screws that have been stripped so they tend to rattle or allow the forward floor board to vibrate a bit on the passenger side. This becomes more noticeable as the speed increases.

I've also gotten some noise coming from the speedometer cable. So you could have the cable starting to vibrate more as the speed increases.
Maybe try and lubricate the speedo cable if it's dry.

Is your check plate on the bell housing still tight? That can also cause a little tinny noise as the car gets more motion.