Hearing Voices

 is a Fallout 3 quest that is added to the game with the Point Lookout add-on.

Return to Desmond
After speaking with Nadine and getting the key to unlock Jackson's sacred praying grounds beneath the Wrecked Seatub, return to Desmond and tell him the news. Of course, Desmond chastises you for not interrogating the Tribal's leader first. Make your way to the Seatub and enter the caverns.

Finding Jackson
The path to finding Jackson is easy enough, follow the torches to his inner sanctum. Although there are Mirelurks in the caves, you can sneak your way through without fighting them. Upon entering the final room, you find Jackson kneeling before a table speaking to what appears to be a holographic talking brain. Let Jackson and the Brain finish, then speak with the Brain. It does not reveal who he might be straight away but explains he is using the local tribal cult as means to destroy a signal jamming device that Desmond is using to restrict his broadcasting signal. Although he is rather disappointed that the tribals take his instructions as destroying his ancestral mansion instead of the jamming device.

Return to Desmond Again
Report back to Desmond in the Calvert Mansion with the information you obtained from Jackson and Professor Calvert in the cave.

The Cogwave Jammer
Desmond asks you to install a jamming device atop the Ferris Wheel near the Point Lookout pier. When you get near the Ferris Wheel, Professor Calvert contacts you and tries to persuade you to destroy the jamming device in a trash compactor near the Ferris Wheel. Whichever choice you make, be sure to retrieve any items left inside the Calvert Mansion as it will soon be destroyed and you'll be unable to visit it again.

Choice 1: Destroying The Jammer
If you choose to destroy the device, Professor Calvert tells you to return to the Calvert Mansion. Upon arriving at the mansion, it is destroyed in a spectacular explosion and you are directed to meet with the professor in his Underground Lab beneath the lighthouse. Before heading there, visit the the panic room beneath the mansion's ruins it contains some good loot. When you enter the lighthouse, head down the stairs that are revealed to you. Desmond will appear from a little side room (that contains more loot) and you can either fight him or help him kill Professor Calvert. If you kill Desmond, use the access card you find on him to go and meet the professor. Otherwise, just follow him.

Note: There is a bug when choosing to destroy the jammer. Upon meeting Desmond in the lighthouse and siding with him again he may end up getting stuck in the next room after he meets you. Even if he gets out of that room he may also glitch and get stuck at the locker room where the Gatling Laser is found. Initiating speach with him will cause him to say "I am desmond" he will be stuck there. If you do not want to load a previous save your option is to kill him and be betrayed by Calvert.

Choice 2: Installing The Jammer
If you choose to install the device on the Ferris Wheel, be ready for an attack by Tribals who will attack you in the streets and from the rooftops. Once you've dealt with them, return to the Calvert Mansion. Upon arriving at the mansion, it is destroyed in a spectacular explosion. Find Desmond in his panic room located under the ruins of the Calvert Mansion. He'll ask you to go with him to Professor Calvert's Underground Lab and kill the professor. Let him know when you're ready and meet him there.

Meeting the Professor
If you decided to kill Desmond, you'll have the opportunity to talk to the professor before he betrays you and activates his army of robots.

Simply killing the professor destroys the robots, but you'll miss out on a lot of XP.

Reward
300 XP