When you complete the first chapter of the game, you will find yourself aboard Sanctuary III. There you will meet up with several familiar faces. Throughout the ship, there are a few hidden echo logs. You can find FL4K‘s echolog when you go down to the cargo bay. If you take the staircase down on the right of the ship you will stumble across a small space. Just around the corner, you can find the hidden echo recording.
I like how these data disks are like old NES cartridges. From time to time your Vault Hunter will blow into the cartridge in order to get them working.