I ran across a weird problem recently with YouTube videos. For whatever reason only some YouTube videos lacked audio. Luckily, I found a reddit post that had a possible solution for a lack of audio when playing some YouTube videos.
I was having this problem on Windows seven professional. I had an older Sound Blaster twenty four bit sound card installed on a desktop computer. I went into an audio control panel and changed speaker configuration from 7.1 to 2.
For whatever reason my default speaker configuration was set to 7.1, even though I only have two speakers and one woofer. You can potentially fix this problem too. You want to go to an audio control panel.
On Microsoft Windows 7, you click your start button and then select "Control Panel". Look for an "Audio Control Panel". You may not have an audio control panel.
Search for or look for your sound cards control panel item. For example look for Sound Blaster, Realtek, etc. Go into this control panel item and look for speaker settings.
If you do not have more than two speakers and your sound card settings in Microsoft Windows 7 control panel is set to more than two speakers, than this might be why you do not hear audio in some YouTube videos. When I changed speakers from 7.1 to 2/2.1 on my Windows 7 machine, I was able to hear once again audio from YouTube videos. You may not have an audio control panel or an item for your sound card in control panel because sound card software was not installed.
You can always install software that came with your sound card or look for software for your sound card on the Internet. These tips can be used on other versions of Windows ie. Windows XP, Vista, 8, and 10. The exact steps to get into an audio control panel or sound card properties will be different.