how long has this been happening for?
are you a new to ED by any chance? as this is your first post are you using RealTek audio.. do you have auros 3d\radar audio installed if so disable while running ED, this should be as simple as terminating the app from the system tray. ive found i get a better sound experience with the windows generic audio drivers
if you use creative audio then they have similar apps they like to use which can also be terminated form the system tray
both of these apps try and create a more "realistic" sound environment but can cause sounds to decrease
ingame you should also try playing arround with the sound settings - iirc i found the night time mode gives the bigest boost to audio whilst some of the others leave the audio some what muted
other than that try right clicking the speaker in the task tray and selecting sounds > right click your sound device > properties > select enhancements > tick disable enhancements then select spatial sound and set to OFF
you could also try ticking "give exclusive mode applications priority" and "allow applications to take exclusive control of this device" - if theyre already ticked then try unticking - under advanced