Whenever the Ender Dragon is on top of the exit gateway, it will make incredibly loud roars. They're so loud the sound goes onto overdrive and will distort very severely. This is by no means proper sound behaviour. This type of sound can really damage speakers, and most importantly players' ears.

To replicate this just try and get close to the Ender Dragon while it's on the gateway. (Attachment pic for reference)
Use headphones.
In no time, it will roar, and the sound will be distorted because it clips and overdrives.