Feedback and echo in the recording can happen if your microphone is picking up sound from your Mac's speakers. There are a few ways to prevent this:
Move the microphone further away from the speakers.
Reduce the Mac speaker volume.
To eliminate any echo or feedback effect completely, use headphones or a headset instead of the Mac's built-in speaker.
Keep in mind that an echo can also originate on the caller's end if they are running into the same situation.