It seems we have the same problems with our tablets. On mine, the brightness is maximum at around 15%. I can also hear some noise from the speaker, but only when the tablet is plugged in. I also experience crashes and reboots along with the noises.
I finally gave up and returned the tablet to get it repaired. I suspect those problems are coming from the battery. Btw, you'll probably notice a very low battery life with apps like Netflix. Those issues can't be resolved with a firmware update as they are hardware related. I'm sorry to be the bearer of bad news, but your tablet is probably defective.
As the noise is concerned, I hear it when I have low battery and when I am looking at website.
And luminosity, I can't have a dark screen. It's like I can set the luminosity between 70% and 100%.
I'll wait than a member of my family in law go back to China (Maybe next year) in Beijing. I'll ask him to go to the shop to repair it.
I'll maybe go to Shanghai in november, so I'll buy the new voyo a18.