Ahahah, this reminds me: after I learnt unicycling and started practising it on longer paths, I started hearing a weird regular "tick" sound from somewhere in the uni(cycle). I was wondering if something's broken, but it was hard to "debug":

- the sound obviously stopped when I stopped riding,

- just turning the uni's wheel on the ground didn't seem reproduce the noise,

- you can imagine it's kinda not very easy to look down and esp. reach for various parts of the uni when you're riding.

At some point I finally managed to look down for long enough to discover, that it was the sound of my shoelace flailing around and hitting the shoe with every turn of the wheel... I realized that this sound must be there even on a "normal" bike, but uni is apparently so much quieter...