There are images of some helmets where you can see a Lemo plug just poking out of a camo pouch like the one
here which leads to a rado-mic transmitter pack that's inside the pouch, probably something like this one.
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picture001.jpg [ 26.82 KiB | Viewed 868 times ]
This is very noticeable throughout the scene where the squad encounters the Aliens for the first time in the Atmosphere Processing Station.
I think the packs would have been used to record dialogue, otherwise why fit them? It's interesting to note that Wierzbowski doesn't have a transmitter pack fitted; most likely because that character doesn't have any dialogue.
You can also see this in this thread
here.
Harry