Crackling usually means that at least one of your speaker cones are ruptured. This can happen when you run the volume too high and with certain recordings that produce volatile vibrations. Standard speakers with Macs are unbelievable but they can still be pushed to extremes and can still be damaged.
Crackling can also be caused due to a loose/bad physical connection. On your sample, it looks like your speakers are internal; but if the speakers are external then make sure that your connections are properly secure. if they aren’t external (they are the Mac OEM internal) then you’ll probably have to take it to an Apple Authorized service shop or send it to Apple for service.With the value of your computer I wouldn’t attempt trying to repair them yourself…even if you’re a trained computer technician; you’ll void any warranty that you have on your Mac Book.
Crackling speakers can be the result of damage to the computer. if you’ve dropped your MacBook or rattled it during transit then this can damage your speakers; you’ll have to have it repaired.i If you’ve spilled any liquid or exposed it to prolonged sunlight, extreme temperatures (e.g., outdoors when it’s very hot or very cold) then this too can damage the speakers. If you have ever had the computer speakers close to strong magnets; then this can also damage them.
Try simple methods of triangulation. Test the speakers on several different song tracks; adjust the volume to different levels e.g., low, low very low, then medium and medium high. Then try making changes with Garage Band or a good equalizer app like Bass Booster.
All the best and I hope that you can resolve the issue. I know how worrisome that can be