There are twp reasons this could happen.
First one is if your connection is not fast enough, hence not able to transmit the voice data as soon as it should.
The second reason is that you might have audio issues is your microphone - not being fully compatible with Flash. The way you can find and avoid this is by testing out the microphone in our Test Window which popups when you try to share your mic. This is where you can hear yourself and see how others are going to hear you as well.