[Serusers] Problem with Voice quality, please help

Hi All,

We made a VOIP application for PDA's (PALM OS) and we are using both SER and Asterisk. SER is SIP proxy and it routes all the calls to Asterisk. On SER we have RTPProxy also. My problem is that I am getting a weird noise or disturbance for all the calls at an approximate time interval of 100-120 seconds and we are getting this noise consistently. After 5-10 seconds everything will be fine till next 100-120 seconds. We are using GSM codec on client side with GSM voip provider. Can you please tell me where it is going wrong and where can I change or improve things for better voice quality? Is there any echo which is causing this?

Thanks, Manoj.