Incredibly frustrating user experience and that you spend the time creating a video and I've now exported literally dozens of times trying different things and it always has audio glitches. If I don't change anything they're always in the exact same place. If I go back and try to mess around with the timeline or remove and re-add clips, sometimes they are in different places. But the fact that it happens in the exact same spot over and over again makes me think it's not just a random occurrence during the render like something happened on my phone that grabbed some CPU time or something.
I've even tried exporting to premiere pro since I'm a full Adobe CC subscriber, but that was also a pretty brutal experience in that the audio for some reason came over all mashed into one track rather than separated the way I had it in Rush and, more importantly the levels were completely different and so it was maxing out into the red for every single track on every clip and the background song. You could definitely hear the poor quality and I started trying to reduce them individually, but then realized that the tracks had been matched together and I didn't have control of this one and there was literally audio playing that was nowhere on my timeline at all whatsoever. I have no idea where it was coming from. And I certainly couldn't control it.
What device are you editing on and what operating system?
Open the source video that is causing you issues in the free download MediaInfo. In MediaInfo, set View to Text and then copy this text and paste it to this forum. Once we know the exact specs of your source video we'll have a better idea what's at work in your project.
What device was your original video recorded with?