No , you won't hurt anything to continue playing. In fact, I don't think there is really anything wrong with the reed. As I understand what you're saying is happening: if you hold the bass button in , and sound the reeds until you completely run out of bellow, you hear at least one reed continue to viberate. Is that correct? If so, it is most likely the large basson bass reed. This reed is very large and the tunge of the reed is "heavey" , so once it gets moving, it will continue to viberate for a short time after the air pressure is stopped.
You probably don't notice it when you're playing in a natural state because when playing naturally, you will let off of the bass button when you stop.
If you hold the button open when you stop the bellow action, it's like squeezing the handle on the garden hose, after you've closed the water valve. Water continues to come out the nozzle until the the pressure bleeds off.
Make any since at all ????
Jude Moreau

Jude,
You're understanding me correctly, and what you say makes sense.

When I've played other handmades in the past, I've never held the bass and emptied the bellows (and it isn't something I'd really try to do anyway), so the rattle isn't something I've encountered before.

Thanks for the wisdom.
Jude

Newton's law of motion.