We’re happy to hear that you are interested in using the module as a teaching tool! I’m sorry to hear that you are having trouble with the Mozzi library. I am not familiar with the Mozzi library but I was able to replicate the sound you posted in the video.
It sounds like that this might actually be an aliasing issue which can be experienced at higher frequencies. I noticed that by decreasing the frequency, the sound went away. I found some documentation on the Mozzi website that discusses these potential issues. I’d recommend trying to find some Mozzi users that have experienced these issues. I hope it works out for you!