It's quite simple,
Once you've rooted, you should use any "root" capable browser, go to the following directory:
Then KILL/REMOVE/SLAUGHTER that m*@#(&@$ bootaudio.mp3 file,
Reboot, and you're good to go!
(Actually this was also a reason I worked damn hard to remove, ****ing sound is awful, I DID however replace my entire system sound set to the 'sheikah slate' from Zelda: Breath of the wild)
I have change the bootaudio.mp3 file with another one(intro from metallica song, about 10 seconds) and when I restart the smartphone, appear only the Logo Blackview and did not open.
So I fix it by flashing again the stock ROM.
How did you do it?
The song must has the same duration like the default?