I believe we have already heard some of their "communication." Do you remember the pings that Enoch and Isaac were hearing? I think it was the C-probes exploring the area. Enough information has gotten out by now that the first priority of the C-probes could easily be to seek out underground installations. The pings could be the radar searches. We know the probes use radar, it was just confirmed in a recent post by Zachary, so it is not at all far fetched to believe they could taste radar from the C-probes.
If I remember correctly, 'as' said there would be many of the C-probes. They could be scattered over a large area trying to use their radar in a form of telemetry to map out the underground structures. Once the tunnels are identified, they may use "direct" means to enter. The Ipsolstai had better be prepared for sudden breaches in their facility and the loss of atmosphere that may entail.
BTW: the caption Daniel sent with the image was "ping ping ping" which I see as clearly intended to mean the pinging is coming from the ship or its occupants.
Koala, Captain, Team Andrew