I've not done DMT but I have done 5-Meo-DMT and I heard the sound. It was like tinnitis only a lower note somewhere below middle A and the sound was from within, not from the ears. I'm agnostic, I do not know what to believe. But some believe that sound is the sound of the vibration of universe. Some call the sound "OM". Some even consider it the voice of God.
Your mileage may vary.
This garden universe vibrates complete.
Some we get a sound so sweet.
Vibrations reach on up to become light,
And then thru gamma, out of sight.
Between the eyes and ears there lay,
The sounds of colour and the light of a sigh.
And to hear the sun, what a thing to believe.
But it's all around if we could but perceive.
To know ultra-violet, infra-red and X-rays,
Beauty to find in so many ways.
Two notes of the chord, that's our fluoroscope.
But to reach the chord is our lifes hope.
And to name the chord is important to some.
So they give a word, and the word is OM.
Quoted from the Moody Blues song "The Word" for purpose of commentary as permitted by the Fair Use doctrine of US copyright law.