Loud beep followed by a decrease in volume

Recently, whenever I play music or video a little below half volume on my iPhone 6, a loud beep occurs (not always the same pitch or length), followed by an immediate drop in the volume and it slowly climbing back up to where it was. This happens one to dozens of times throughout a 3-4 minute period. Here is a link to a video displaying that beep: https://youtu.be/kVTP3d4j128 Does anyone know what this is and how to fix it?

Thanks,

Josh Woodward