Core Issue
It is common for packet loss to occur in packet networks and not result in perceptable sound problems. If occasional pops or clicks are heard, then check your sampling rate. Longer sampling periods, for example, G.729 with 30ms sampling, offer additional bandwidth saving. However, there could be a trade off in voice quality as a loss of a single packet can be enough to produce an audible click or pop, whereas in the case of 20ms sampling, a loss of two consecutive packets would be required.
This popping sample is similar to the popping that might be heard in this case, but more severe.
Resolution
Change the sampling rate for the codec to 20ms. Also attempt to determine the source of packet drops so that these can be resolved. Issue the show call active voice command to assist.
If the packet loss is more severe, then usually the sound is more like choppy or synthetic voice. In this case, it will be necessary to identify the source of the packet loss and address it. Issue the show call active voice command to identify high jitter values and non-zero packet loss, and ensure that Quality of Service (QoS) is correctly configured. For more information, refer to the following documents:
