I've seen a few people who own the 2018 macbookpro to face this issue together with the fact that the speakers crackle. The issue other than the fact that the speakers cracks is that whenever you play like a youtube video, sometimes audio will cut, it will buffer forever and no matter what you do you can't play it again. You have to restart the application for the video to load properly. After testing again and again, it can sometimes be triggered by a different application, like opening quick time player, causes the audio on the youtube video and the .mov video itself to cut audio and not play.
It only works again after relaunching the application. I've reformatted/factory reset the computer, reinstalled MacOS, the crackling has disappeared (so far I haven't heard anything in 12 hours of usage since) but the audio cutting still presist, however with youtube video, I do not need to restart the application anymore but by simply opening a new tab. (it still happens with like spotify etc).
To note, I've sent my computer into an authorised service center and they were unable to diagnose any issues with it. It seems that my friend who also got his 2018 macbookpro from the same shop at the same time, the 1st batch in country doesn't have this issue.