This is a bug that was in OG MCC as well.
Game: Halo2 - Anniversary or Classic
Issue: Radio transmissions from on screen characters won't travel with player. (This wasn't an issue in H2 on OG Xbox) Example: If Sgt. Johnson has an on screen model, and you walk away from him, for certain scenes (see clip) the radio transmission is supposed to be heard. However, in MCC, the transmission kind of just sticks to the character's (in this case, Johnson's) vicinity. You can hear him fine if you're right up next to him, but if you walk away, the voice doesn't travel.
Repro steps: Any scene where this occurs, really. Johnson at the beginning of Cairo Station saying "LET'EM HAVE IT!" but be close to the bulkhead. The clip below (Outskirts). Sgt. Banks yelling at the Scarab (New Mombassa). Etc.
I found a similar issue in Mombasa streets, but actually opposite. I could be wrong, but I thought I remembered that if you walked closer to Johnson as he is talking in the pelican in the courtyard his voice switched from radio to his actual voice. When I played last night it sounded like he was over the radio even when I was next to him.
Like I said, I could be wrong about that being different. I do know this was a feature in H3, it is possible I am confusing them.