the sun sounds like a big old grumpy man, that only knows how to mumble. If you speed up 40 days of recording into a few seconds you hear the sound recorded in the video from above.
In any case, the mechanical waves that fly through the Sun day in, day out are the source of that sound. The sun is everything but a quite place and sooner or later you will see a ton of such symphonies created as a result of EM waves or other phenomenons.
Hail to the Sun.