(paraphrasing)

"Hmm. This system was used to detect undersea vessels in order to guide them in for docking. And it's still active! And.... there's something down there. And it's HUGE..."
- Ghost

This audio is from an inspection point on Titan. The specific point is located near the tank public event on The Rig. If you fast travel to the rig, walk to where the public event flag is, turn around to face the main body of the rig, there's a door pretty much straight ahead of you. Head inside and look at the monitors on the left hand wall.

Added to this audio is the giant object visible behind Sloan when you talk to her on Titan. It's black, and bulbous - almost like a dead insect of some sort. But if you look at the docks it has burst through, it pretty clearly burst out from *below* the waves rather than punched through the docks from above.

Unfortunately, we cannot visit this monstrosity, nor can we delve so deep into the arcology as to see what lies beneath it.

So what lies below the waters of Titan?