It's the game's crappy codec, it's why you should always use your own Teamspeak channel even if the game has great voice chat support.
True facts: our game uses the Steam API for voice chat. It is identical to the one used in TF2, which, for the record, is Skype's SILK codec.
You're welcome.
I know, right? And yet people insist on using fucking Skype or some shit and bitch at you to install it too because "it's easier" or "it sounds better" when it's the exact same fucking codec. Steam's friend list uses the same goddamn codec and people still want you to install Mumble or Teamspeak or whatever for a pickup game. Or on this game specifically, you'll need to communicate with the captain of your ship but he's talking to the rest of the crew on Skype so you only hear instructions when someone cares to hit X to fill you in. Huge pet peeve of mine.