Hello, the topic is getting old, but I just come to bring an answer for people having this problem.
If you have an echo problem on your OBS it could also be for this reason: If you use several Overlay where each one has a Media Request, each one will launch the Media Request individually. For example I was using 3 overlays for 3 different scenes, each with a Media Request, so the music played 3 times at the same time with a few seconds delay.
To avoid the echo, you need to have the Media Request on a separate Overlay to be played only once in your scenes. Other Overlays should not contain the Media Request.
The same problem can happen with Alert Box. You need a special Alert Box Overlay, separate from the rest to avoid echo.