To "turn off" the feedback, follow the steps below:
1. Access the main menu of the game by pressing the Start button.
2. Then scroll through the icons and select Options.
3. Choose Settings Audio and Video
4. Please scroll through the icons until you get to Microphone Volume
5. Select it and bring the volume down to zero.
6. Press to confirm and press the appropriate Back button until you get to the main menu again.
Rocksmith will now automatically save your new settings, allowing you to play without any feedback effect.