@RegitnuiYes and no: as I've been writing it so far, as he gets bigger, the voice/sound he is capable of producing gets larger as well. His telekinesis remains the same level, but he can get really, really loud.
Of course I'm thinking now that an adrenaline rush while asleep would probably also wake him up, so he'd be normal again and have to deal with it. I was also thinking about this being a sort of hint to himself that like "hey, maybe I can do some more impressive things than just scare petty crooks and stuff"
but naturally i leave that up to the GM to allow/veto
I have something else in mind as backup
EDIT: basically just imagine a deafening, hollow echo as this invisible titanic phantom breathes like death itself: not deadly or powerful, but hella terrifying