Hey there, samha48!
Thanks for using Apple Support Communities! We understand you're having an issue with a buzzing sound from your left speaker. We'd like to help.
Let's first make sure your Mac is up-to-date. Here's how you can check, if you're not aware: Update macOS on Mac
If your Mac is plugged in when this happens, let's have you try a different power outlet as well to rule out electrical interference.
Lastly, if the issue still continues after completing the above, we'd recommend visiting your local Apple Authorized Service Provider or Apple Store. You can find them here: Find Locations
If you would like help in locating service, contact our Apple Support team: Contact Apple Support
That should help.
Take care!