What the title says. This started a few days ago. If I’m inside the game, the volume is low. As soon as I press Win and leave the game in the background, I can hear everything at normal volume. Go back to game, low volume again.
I noticed that, if I’m playing some music in Spotify and open Overwatch, the music also gets lower volume. If I close Overwatch, the volume is back to normal.
All my settings are at 100% max. Any ideas?
Not really familiar with your issue, but found an old thread about it:
Thanks! I tried all of that but none worked. It’s really weird.
1. Open " Sound " applet from Control Panel . You can also access it directly using " mmsys.cpl " command in RUN or Start Menu search box. Or right-click on Speaker icon present in system tray and select “Playback devices” or “Recording devices” or “Sounds” option.
2. Now go to " Communications " tab and check the option " Do nothing " and Apply it.
Let me know if it works 
I opened the game today, there was a new patch. Downloaded it. Started game. Problem was gone.
I had a problem where all of my Blizzard games would have reduced sound in game and when I would tab-out they would go back to normal and then I’d tab back in and it would be low again. Been looking for a solution and then I followed your steps and fixed my months long problem thank you much!