You mean this sound, yes?https://www.youtube.com/watch?v=f_-OTZHBIuE
I'm not applefriend but I don't think adding it to the entire site would be a good idea, even if it were optional some people new to the site would find it bothersome and assume there's no way to turn it off and leave. If it was set to be off by default it probably wouldn't see much use, I don't know how much work it would take to implement but it feels like it wouldn't be worth the trouble if no one uses it.
Instead, what if we only had it play on the homepage (https://lainchan.org/
) like how https://sushigirl.us/