Just got the same bug.
Login screen music that starts at login screen, and usually stops once login is successful, doesn't stop anymore.
Music continues to play, continuously looping, until few seconds after game is closed.
Non of in game sound volume options seems to affect it.
Oddly enough looking at the Volume Mixer in windows, sound is coming from Steam Client WebHelper as oppose to game itself.
Muting web helper works.
Just double checked, it is not actually Login screen music, at least in my case.
It just that Steam Web Helper starts with game, and begins blasting Duviri theme at the same time.
Edit: Found where it was coming from (at least for me), Steam Community overlay had Warframe's website open (got plat coupon as a daily login), I guess music was actually coming from the website open in the overlay. Once I closed it, it went away.
