like - it just seems weird that she only communicates in noise. i get that all the non-humanoid voidspawn are different species, and that shes not the first one to not be able to communicate (though gnar's gibberish is at least somewhat recognizable as speech), but it just is kind of bugging me that she can't communicate, and yet vel'koz, a floating mass of orbs and tentacles, can.
i dunno, i might just be getting nitpicky here.
It bothers me too tbh. It's inconsistent with the way previous Void champs were handled and is a result of Riot deliberately making Rek'Sai the one kind of champion they said they DIDN'T want to make: a mindless beast with no intelligence. Especially given that Rek'Sai is intended to be a queen of some sort, I would have assumed that she'd be one of the hyper-intelligent Voidborn overlords that are masterminding the invasion of Runeterra, not just the Void equivelant of a bear.
It doesn't really bother me
The void has creatures of varying degrees of intelligence(vel'koz is highly intelligent,but unable to understand some stuff like emotions,Cho seems to be directly malveolent and doesn't seem to be driven by instinct as much as others,Kha is probably able to get smarter by eating smart creatures,kog is more like a toddler,etc.) Rek'sai however is a creature that can't talk,she is more like an animal.I mean look at our planet.How many species have the ability to talk?It is actually rather surprising that all void creatures so far were able to talk.
You have it backwards. It shouldn't bother you that she can't speak, it should bother you that other who shouldn't speak can. How do void creatures, who lore wise are depicted purely as devouring the life of runeterra, learn the native language anyway? Vel'koz absorbing knowledge could be explained, except for the fact he has no way to speak (as you mentioned).
Likewise I think Sona shouldn't speak at all. Her joke and taunt already are music based, and the same could have been done the rest of the time as well.
So I give riot props for finally stepping it up and making something that shouldn't speak, not speak.
Ok. 
She speaks, just not in a language we can understand obviously.
And to answer the question, no. I like it, it's something unique.
"does it BUG anyone else"
I see what you did there.
I'm ok with it. Now we got our female monster champ quota filled so on to the next champ :)
