| | volume
I experienced the same problem with my Motorola Bluetooth Headset. In my case the people who called me also complained of an echo. After I turned my listening volume down, it solved the problem. The earpiece is in such close proximity to the microphone that it causes a loop effect, thus the echo.
This also explains why it happens to you and not your wife, she doesnt require the same amount of volume to hear.
Try turning the speaker on your BT down and see if it helps.