From Halopedia, the Halo wiki
I got a response from Crazyboy557 and couldn't hear it in YouTube vids. As a matter of course, I'll check on ALL 5 difficulties (easy, normal, heroic, legendary, and the mythical mythic as the game appears to notice it now. I think it might be in an exclusive game. Your descends into screams and gunfire led to about fifty reverts to last checkpoint. Thanks for clearing that part up though. I'll check since its in subtitles. Crazyboy557 said he noticed something similar in the next level.
To be honest, I just made an assumption based on how there were other radios in the level. (bad, I know) If you think there is more evidence of the conversation coming from IFF tag than a non-existent radio, go for it! :)
You may have seen my question about the level Infinity. I found that you added the first radio conservation on said level (the one that is triggered by examining the first IFF tag).Where is the radio you mentioned and how can you hear it and others cannot. (I have the standard pre-order edition.) ;)