When streaming, you need to be conscious of your audio routing, and how audio works in general.
You are capturing your game audio, by capturing all of the audio playing out your computers default audio device.
You are then sending that audio out a stream.
---Now, you are saying you are watching your stream and the sound starts looping/echoing/repeating. Well, if you are watching it in the player in your web browser on the same computer, you are playing that out the system audio, which you are capturing from the previous step. So you are recapturing the events at a later point in time and feeding it right back to your audience.
TL;DR Never watch the stream on the same machine, it will add a fair amount of load to your CPU potentially causing frame drops, and if the shot you have live is capturing system audio, ANYTHING you play audio wise on your system is being fed to your stream, so you are creating an audio loop by doing so. If you need to see what your final stream looks like, you should be checking it on a separate device.