Loid's idle quote when researching Dante (source/Quotes#Research_Dante)):

"Warframes cannot speak, as a rule. Their creator decided they should only scream, or roar, or howl. Dante spoke through his writing, and his voice was beautiful."

That's understandable, as they were meant to be just war machines, so Ballas made them only scream (I'm guessing "as a rule" means he designed them as such?). Just an interesting conclusion given I saw some threads on the topic. Could this have some interesting implications?

As a side note, if controlled by an operator, we can see the operator speak straight through the Warframe (through either transference or directly some space Bluetooth communication, idk.), for example with Teshin in a cinematic early into the war within. This is rarely used though, and we mostly just stand awkwardly when I guess we would have said something.