Hi again everyone.
After fixing the random sound disappearing problem I got an issue even more stressful: the battery more or less at 54% just drops dead.
If I try to boot the laptop at 54%, only after login in, the battery icon shows "54% (30 minutes remaining)". Then I put the mouse over again and shows "54% (10 minutes remaining), I reboot and at the login screen it dies. Sometimes even without rebooting, it just dies without any low battery warning.
If I use my laptop to watch movies from 100% it works perfectly fine: it show the warning at 20% and lasts another half an hour at least. If I use it until 60% and then turn it off and turn it on again after days, this issue happens.
Few bootup programs enable (mainly steam and nvidia experience), issue appearing in charging mode "Balanced mode" and "Full capacity mode".
Also, I cannot use my laptop if I plug it in right after it died. It seems like it has to wait for the battery to charge a little before being able to boot it. That is absurd, every other laptop I owned it would have used directly the power coming from the charger, instead of waiting for the battery to have a small amount of charging.
Anyone else has this issue?
It is incredible that my laptop has all this issues after 3 months of life. I contacted Asus service, if they are not going to fix it I think I will have to change manufacturer. For me it is sad, because I LOVED the N551JM and now I'm stuck with this black brick of misery.