I often have my browser's devtools open since I'm often debugging a snippet. I noticed this message often recently:

Why is Stack Overflow trying to start audio?

Update.

I see it's from an ad?

https://static.adsafeprotected.com/sca.17.4.95.js

Update 2

It happens when this ad appears, From Microsoft via Google.

Update 3

2019-08-15: Official company response after investigation and inquiry. It has been decided that such user fingerprinting ads will be permitted, as they do not violate any laws or regulations.