If you hear your own voice after about 1/2 second, it is often a problem at the other end of the call, not your end. The person either has speakers near their mic or has them turned up too loud. If the other end is a telephone...turn down your volumes. You are getting a reflection from somewhere in the telephone network, and lower volumes will usually help.
If the other person is hearing their voice back or a hollow sound, you have speakers on in the background (turn them down), Mic boost on (a VERY Common problem see the Mixer page) , or WAV is not muted on the record mixer.
You or the other party has Mic Boost enabled or the record (mic) volume has been turned up too loud. Once the volume exceeds a certain level, the peaks of the sound waves get clipped off, and the result is unintelligible. For Internet telephony, use about 50% volume on the mic with boost off.
Dropouts and Static:
This is usually related to speed or traffic problems. Remember, that the problem could be at the other end or anywhere in between, and it does not mean that your internet connection is bad!.
Turn off all of the controls in the playback mixer except WAV . Some sound systems will pick up a hiss from the unused inputs. Having 3D sound enabled (Advanced button on the mixer) will also sometimes cause a hiss. If you identify the culprit you can mute that channel.