I am guessing the answer.

Mustered seed is a ball. This also contains water. When we put this seed in hot oil, water becomes steam and tries to escape from the seed. Now if the seed is unevenly heated then it gets propelled by escaping steam. The noise is created by the steam. For the seed the bottom part is hotter than the top part. Therefore, the steam escaping from the bottom pushes it to the top.

I hope that I am write.

There is no specific pattern. Either they follow convection pattern of oil or the motion due to escaping steam.

Thank you sir! Sounds right to me.