I tried adding all 3 modules to the Direwolf20 pack, but it resulted in sound working normally on the main menu, but there is no sound whatsoever once a world is loaded - even in the menu. The sound returns when exiting back to the main menu

That's wierd.. A couple questions:

• What version of Mekanism are you using?
• What version of the modpack are you using?
• Do you have any logs available?
• Is this singelplayer or multiplayer?

Wow, I just downloaded and tried it again and it works fine. I can't imagine what the problem was before. Thanks anyway

If anyone ever sees this, try redownloading and reinstalling the mods

I have the same problem, I'm using FTB beyond modpack, with Minecraft 1.10.2 version, and I've added Mekanism mod to it. When I load any world, my bluetooth headphones just stop working, not just in Minecraft but anywhere. And as long as my world is loaded, it stays so, but when I exit the world, headphones start working again.

As I said, try removing Mekanism, play, and add it again, redownloaded. If this doesn't work, try making a new profile, and, if that doesn't work, restart your computer.
If it still doesn't work, consider reinstalling Minecraft.
If it still STILL doesn't work, come back here.

Of course I did this before commenting. Also I've tried different versions of modpack and different versions of mod, new clean installation of client in a different location and even different windows profile, still the issue stays.

Did it work before you added Mekanism? (it's not clear from your comments)

Yeah it works well without Mekanism, and the problem goes away as soon as I remove it.

Well, I'm out of advice. If none of that works, I guess I'll reopen the issue. Good Luck!