Explain the SSj Transformation and Aura sounds with In Universe logic

[DSB]

Obviously they were for the anime, but i suppose they are such an integral part that maybe even toriyama thought of them while designing a new transformation [like SSj2 Lightning]

Explain them with in universe logic

[VegettoEX]

They're a manifestation of ki, and as the power grows in strength so too do the external characteristics grow and change (such as visibility and sound). It's like the sound of cold water hitting a hot frying pan, or in this case the previously-invisible energy entering the physical realm.

[DBZ Macky]

I remember when I used to watch Naruto, everybody made a big deal out of how bad-ass and strong Sasuke's Chidori was, since it was clearly visible (which regular Chakra is not supposed to be) and it sounded like a 1000 birds chirping... or something. So it's probably the same concept with Dragon Ball's Ki. The energy these buff guys wield is so damn powerful that it converts the residual energy into sound and light.

[Son_Gohan]

Obviously they were for the anime, but i suppose they are such an integral part that maybe even toriyama thought of them while designing a new transformation [like SSj2 Lightning]

He did. Not sure if you noticed, but transformations are usually accompanied by onomatopoeia/sound effects in the manga. But it varies a lot and is not exactly consistent as it is the anime.

[Boo Machine]

They make those noises with their mouths, much like how a child will make motorcycle sounds while on his bicycle.