When i use new minecraft launcher for the first time - i try to play 1.6.4. It downloads files (like 1.6.4.jar) and then the game starts. When i try to play - there are no sounds, but in mc options and windows it is set up to 100%.
Then, i downloaded an old launcher from https://minecraft.net/en-us/download/alternative .
And pressed "play" there. MC game starts with no problems and all the sounds.
So, i think, that there is a prolem with new mc launcher.
Duplicate of MCL-6280. The legacy assets index is apparently broken, so very old versions of the game using it won't work. According to that ticket, it will work if you launch with the old launcher first and then switch to the new one, though.