Please no. The sound makes this one of the best mounts in the game. It's not a problem, it's a feature. I love it and was super pleased to experience it.

There was a bug when it first came out where the sound would play for all characters on the select screen but that's been fixed.

Is it possible to tweak this horse's sounds? Every time I summon it or press w, my ears bleed. I don't know if the same problem appears on all Mind-shriven mounts.

That was the reason why I didn't buy this mount, even though I like this skinny horse body model
If I remember correctly, originally Mind-Shriven Horse had even louder voice, and the volume for it was reduced long time ago after many complaints. For my taste, this horse and Death Hounds are creatures with the most awful voices
If it was possible to have settings where you disable the mount's voice (even if it would be just for you as owner), that would be great. It would allow all players to use this mount, no matter if they enjoy the voice or not.

Mind-Shriven Wolf doesn't have this problem, because he uses normal wolf voice with lower pitch and some echo: