At Discord settings there's a few options that you can enable at "Voice - > Advanced Tab", regarding "noise removal" "echo removal" and such, have you tried enabling those? Also check if your headphone "ouput" volume is slided to 100, I don't mean the "main volume" that you listen but the volume that you can enable to be reproduced by your speakers or any audio device just like a Microphone, try also checking that at "Sound" settings on your Windows Control Panel. "Right Click on the Device, then click on "Properties" and check if there are extra options enabled, if you don't know what each one of the settings does please do post your "sound settings" print so we can figure it out what's going on. Also I'm not sure what Headphones are you using but does it comes with a audio card built within that has separate drivers or panel to tweak settings? If so, try checking that as well.