To unlock the "Whisperer" trophy in "The Bridge", you need to complete the level "The Library" (the second level in Chapter 1) without making too much noise.
Luckily this is a little easier to determine than it sounds -- as long as none of the moving objects make a significant sound during your traversal (no vibration on the controller, assuming you have that on, or a loud bang if you don't) you will unlock this trophy at the end of the level.
Slowly rotate the level a full 180 degrees with LT so that the level is upside down. Before you get to that point you will want to start feathering LT with smaller pulses compensated by small pulls on RT to stop the book in the centre of the level sliding across the level too quickly. You want the book to land gently. Now walk left all the way off the edge (the hero shouldn't make enough noise with the fall to be a problem.) Now you need to rotate the level back around 180 degrees with RT, again slowing right down when the book starts to move a tiny bit and compensating with LT to gradually bring the book to rest in its original position. Grab the key and walk to the door, and the trophy will unlock while the next level is loading.
If you are sure you met the requirements on a second or further attempt, you may need to quit out of the game completely, restart the game and restart the level. Additional attempts without resetting the game seem to cause some problems with trophy unlocks.