The Minor Illusion cantrip lets you create either an image or a sound for one minute. The text for the sound case says:
If you create a sound, its volume can range from a whisper to a scream. It can be your voice, someone else's voice, a lion's roar, a beating of drums, or any other sound you choose. The sound continues unabated throughout the duration, or you can make discrete sounds at different times before the spell ends.
When I create "a sound" as "discrete sounds", do the sounds have to be related to each other in any way? Can I create a lion's roar one moment, and a beating of drums the next? Can I start with the lion's roar, and then change my mind partway through the duration and switch to beating drums?
The confusing part is the use of the singular term "a sound", and the lack of clarity as to whether the choice of sound has to be specified when you initially cast the spell. I would not normally consider a whisper and a scream 1 minute apart to be the same sound. However, the wording suggests that it might be possible to cast Minor Illusion once and then get 1 minute of arbitrary unrelated sounds without using any additional actions (or even performing any additional somatic components or consuming bonus actions a la Unseen Servant).