The beeper on the HP-71B is pretty cool. You can do lots of fun 1980s retro sounds with it. I had some fun with that in my dice games for the 71B. I even had a "raspberry" sound for when you zeroed out yatz. :)
When I got back into RMB, I wasn't expecting to find anything as capable on my 9816. I vaguely remembered that the beeper on that machine is severely limited. Indeed, I find that RMB 2.0 running on a 9816 is limited to some oddly spaced frequencies. These appear on page 27 of the BASIC Language Reference. They are mostly useless for music, and limited for audible prompts. A lot of them are too high to listen to comfortably. But I found a use for the first three frequencies greater than zero on the list.