In issue 151, Eugene got a radio transmitter working and decided to see if anyone was out there. At the end as he was going to turn the radio off, someone contacted him and I would like to discuss who it could possibly be. So here are a few ideas I have of who it could be.
I say this theory because the person on the radio sounded extremely professional and most likely the government would have access to radio transmissions during the apocalypse. Also because we haven't really seen much government activity in the comics and the beginning of the second half of the comic book series seems pretty fitting to include them now.
Maybe The Whisperers are trying to recruit more people or they are trying to spy on Rick's group by listining to them on the radio.
A New Settlement
So far, there is 6 different settlements that are still active so this wouldn't be suprising.
Maybe Eugene is losing his sanity because he lost Rosita and his child, like when Rick lost Lori and Judith and he "talked" to them on the phone.
Those are just a few ideas I have on who it could be. I will update this later so it looks better and feel free to say who you think it could be in the comments.