Not helped by the nonsensical UX. Why would a user expect changing a selection in a dropdown to start playing sound?

I know UX isn't the name of the game here, but I think that's the part that made me shit myself

Absolutely this.

I have my headphones at what I consider to be a reasonable volume level, yet this website was so loud that my ears are ringing.

Is it just on my end or is there some explanation for the (perceived?) higher volume?

Agree. I was listening to something else which had reasonable volume and this absolutely blasted my ears at an uncomfortable level.