Collect the First, Second and Third ECHO in The Secret Chamber in Borderlands: The Pre-Sequel!
Collect the First ECHO
To collect the first echo shoot the green glowing part of the elevator opposite the air bubble:
It will be easiest with a sniper rifle. Then supercharge the jump pad by shooting the box that is connected to it and use it to jump up to the platform. Now you can collect the first echo.
Collect the Second ECHO
To collect the second echo run into the jump pad from the side and keep moving towards the metal beam above you:
Once you are on the beam you can jump up the the platform and collect the second echo.
Collect the Third ECHO
Collecting the third echo is easy, go to the place marked on the map and shoot the enemies. The echo will drop.