Jukebox Echo

I found a 3-year old thread that discussed this, but the issue was never answered. I have a multiple monitor setup that I use for face-to-face tabletop gaming with my group, and I use Roll20 for its dynamic maps, lighting, graphics, all the bells and whistles that make our games even better than before.  I have one monitor set into the tabletop as a playing surface, where I am running a browser logged in to Roll20 as a player (full screen mode, with the sidebar hidden so only the map is visible).  Meanwhile, I have a second monitor on my desk that only I can see, with a browser logged in to Roll20 as the GM. The problem comes when I try to play any sounds through the Roll20 jukebox.  As soon as I hit "play", the selected track(s) will play twice, one just slightly delayed, for a very distracting echo effect. I have tried adjusting the master music volume levels on both the player browser and the GM browser, concurrently and independently, with no success.  Is there any way to address this?

If you are not entertaining any remote players, check to make sure that your microphone is off. You might be picking up your own music playing and re-broadcasting it?

Does each monitor have speakers or is it just a set of speakers and mic? As Keithcurtis mentions, it sounds as if a mic is picking up the sound and replaying it.

Just one set of speakers, and the microphone is indeed off.  Good ideas to seek diagnosis, but unfortunately, that's not where the problem seems to be.