GIANT VOICE is the emergency communications system that is used on military bases. (see: http://www.frontlinewarningsystems.com/pages/military-giant-voice-systems)

The phrase 'giant voice' sounds somewhat odd in his sentence, and it's capitalized too. I am not a native English speaker. I am not a Q-Larper. But to me the phrasing sounds odd, giant voice is not a term I'd normally, instinctively grab onto in common parlance.

If this is a keyword, it also changes the context of his Tweet.

His tweet doesn't make much sense in the context of a Biden administration. Of COURSE we will be treated unfairly. By virtue of having the usurper admin alone, we are hurt and treated unfairly. Of course we will be silenced.

But if this is read within the context of GIANT VOICE (the military system), it becomes validated by the protection which can be offered by the military to us against those who silence us and disrespect us. E.g.: 'You've been abused, lied about, some of you even killed, but from now on, no-one is going to hurt any of my patriots because [the military will intervene]."

Coz otherwise, how can it be true?

Maybe I lost the plot. But I find this keyword interesting. Either way, I still love President Trump. ALWAYS.