Hearing phantom voices

[Lib Feathers]

Three times this has happened to me now - I wonder if anyone else has experienced it. I've been on a friend's ship out in the middle of the ocean, just the two of us sinking ships, and we hear someone else speaking. There are no other pirate ships around. He seems to be talking to someone else so we only get his side of the conversation, but I finally tried talking to him last night. I asked where he was, he said "a jail cell", but he might not have been talking to me, it could have been a coincedence.

I took a screenshot that shows we're the only ship in the area, there's 2 people on the ship, and yet there are three people talking. Anybody know what's going on?