When i join voicechat in Overwatch the Sound of the game radically changes. The bass, the highs and everything else sound completly different and in my opinion - worse. When i exit voicechat it all goes back to normal.
I tried that on two different Desktop PC’s (one with Windows 7, the other with Windows 10, 1803) but the problem is the same. I also made sure that the settings for Windows communication devices are correct (“do nothing”). The Ingame Switch for Dolby Atmos doesnt solve the problem.
Is this behavior normal for the game or is there some hidden switch/setting in Windows or Overwatch that changes the Soundscape? Maybe somehow tied to my profile?
I rarely use the voice chat, nonetheless, when I do I never had any issues.
What audio device are you using?
What are your in-game audio settings?
I tried the default Audio settings but that doesn’t seem to change anything. I use a normal Jabra Headset but i tried a different from Creative too just to make sure it’s not a hardware problem.
Do you have a specific device selected under “Playback device” selected, or is it set as “DEFAULT”?
And what do you have selected under “Voice chat devices”?
I used my headsets as standard device so that windows automatically changes to that devices when i plug it in.
But i just found out something profound - just for fun i tried some wired headphones that connect via standard audio jack - suddendly there were no sound changes when switching to voice chat (the dont have mic but anyway). I also connected my Apple Airpods via bluetooth to try if the problem is present there - with the Airpods there is also no change in soundscape. So it seems to me that the problem has to do with USB. It’s still weird that this happens on two very different PC’s and with two different Headsets. Any ideas left ? 
I can’t really help you here.
I use speakers, which are plugged through a USB microphone with an audio jack port, as well as a PS4 earphone plugged in through a standard audio jack port. I didn’t notice a change in either.
Although, I’m uncertain if I actually used the voice chat while I used speakers, so I will check that in a minute…
And I did a match of quickplay on speakers, which are essentially plugged through a microphone which is plugged through USB.
Either the game doesn’t like to output directly through USB or I have no idea what could be the issue.
So it seems that i can solve this problem by deactivating all other sound devices except the headset in the windows sound settings including my normal speakers. afterwards there are no sound changes when joining voice chat anymore.
I solved this by going to sound settings > Format > changing to 1 channel