It's an issue with Imgur and how their media files get embedded on the forum. It only happens when you embed an Imgur file with the [MEDIA] tags and try to put it in a spoiler (using [IMG] tags on direct links still works fine.) I think Imgur must have changed something recently with how their files are embedded on other sites because it seems to be broken on every forum that I've tried.
Even embedding in Discord broke, to a point, for a while now.
Imgur tries it's best to fix things, but there always has to be something that catches fire in the process... pretty much how coding works, overall.
Someone just drove by my place blaring Phil Collins' In The Air Tonight at the exact moment the drum break happens.
Psh, their timing can't possibly be that good. They just have a loop track of nothing but the drum break (no complaints, I'd do that too).