I think I might know the reason
Originally Posted by mazdamiata210
Pretty much every time I make a phone call I have people complaining about feedback they're hearing or an echo of what they're saying to me. Is anyone else experiencing this problem? Is my phone defective?
The note 3 has multiple microphones so it can cancel out back ground noise. It expects that your voice will be mainly be picked up by the lower microphone next to the USB port. If you sometimes block that microphone with something like your hand, you will mess up the noise canceling algorithms which could result in the echo. Try blocking and then unblocking that lower microphone with your hand and see if you can make the echo appear and then disappear for the caller. My guess is you will find the source of your echo.
ATT Skyrocket, ROM: Embryo 5.1, Radio: UCLF6, Kernel: CYMBALINE-RD03-2.6