Problem with Intermittent Sound on Trixbox 2.6.1


When using trixbox to make calls, am having problems with “dead spots” in the signal. The details of the problem are as follows:
*The sound will be interrupted for a second and then return
*The problem is apparent on both internal and external calls
*The problem can be heard both on two party calls, and when listening to the IVR from outside
*The problem is intermittment – sound may be fine for a few minutes, and then the users might encounter several dead spots within a single minute

What We’ve Tried So Far
*Have restarted Asterisk
*Have restarted our Octasic SoftEcho software
*Have restarted the server
Still the problem persists

Configuration Details
*3 ghz P4 processor
*2 gb Ram
*2 x 160 gb hard drives in a level zero software raid

*OpenVox A400P configured with 3 FXO and 1 FXS port

Telephone Connections
*China Telecom POTS lines
*No SIP trunks

*Trixbox 2.6.1
*Octasic SoftEcho software

I suspect that the interruptions could be caused by some corruption in Asterisk/Trixbox, but am not sure where to look. Any advice would be appreciated.