Crackling/Buzzing Audio.

Hi,

If your MacBook Pro has intel processor, resetting NVRAM could solve audio related issues if you haven't try it yet.

Reset NVRAM or PRAM on your Mac - Apple Support

You have not provided enough details such as the exact model of the Mac and version of macOS being used. You can get this information by clicking the Apple menu and selecting "About This Mac".

Also, does this happen while using the laptop with just the battery or only when using the charger?

Are any other devices connected to the laptop when this happens? If so, then maybe one of them is causing the problem.

Are you sure the crackling/buzzing is actually coming from the speakers and is not a fan or drive making noise? Try muting the audio and try connecting headphones to see if the noise stops or whether you also hear the crackling/buzzing in the headphones as well.