[Freeswitch-users] mod_conference background noise

Hi All, since yesterday i make some tests with the mod_conference and it works pretty good, but i have on all conference member phones a background noise. All configuration changes with the energy level, frame size (interval), volume of microphone or listening do no fix the problem. The conference member calls works with PCMA/8000 ptime 20. In the wireshark trace i can hearing, the background noise come from the FS to the HiPath 3000. You have any idea for correction options? Thanks