A fart that serious wouldn't seem real, and that goes double if it appears that you unmuted specifically to make the noise. Just tell people it was a soundboard.
You never know, this could have been a class about finance. Jim Cramer got disgustingly far using a soundboard. Also by grifting investors with his hedge fund, but mostly the soundboard.
You'd rather be the person who decided to randomly unmute to share your actual factual filthy self? At least a soundboard is just a poorly judged joke (that actually landed, if the teacher laughed). Or you can be a fart pervert.