Hello KarolinaNaja and welcome to Apple Support Communities.
I see you are having an issue with distorted sound on your MacBook Air.
You mention that it happens with "certain videos." If this is only happening with some videos and not with audio content in general, the issue is most likely with either the actual content or with the streaming connection. You can isolate that by reloading the content that is distorting or trying it in another browser. But, again, unless this is happening consistently across apps and with various types of media, it's not an issue with your Mac.
Cheers.