Try holding lightly onto the fulcrum, dropping your stick from a height of .5". Alternate with your other hand, overlapping the buzzing so that there's no pause in the sound. That's how you do a quiet bounce roll. Easy peasy. That's how you want your rolls to sound. When you play with heights of more than .5", you start the stroke with pressure on the fulcrum, "pressing" the stick into the head to get more notes out of it quickly, loosening the grip when the stick height gets to the .5" height. Try to smooth out the transition from the pressed notes to the released notes.
This is the classical version of the multiple bounce roll, called the "press-release" technique. Smoothest rolls you will ever produce, but it takes time and lots of practice. Good luck!