Fix Asterisk GSM Noise

I run an Asterisk-based PBX on Linux that handles SIP/RTP traffic through a Synway GSM gateway. During live calls we hear persistent background noise that degrades voice quality. Static, echo, and other artifacts are not the main problem—the line simply has a constant hiss that makes conversations tiring and unprofessional.

I need someone who knows Asterisk, Synway hardware, SIP signalling and RTP media flow inside out to:

• trace the source of the background noise, whether it sits in the gateway, codec choice, gain levels, jitter-buffer settings, or network path
• apply and document configuration tweaks (Asterisk .conf files, Synway parameters, codec packs, echo-cancellation, AGC, etc.)
• prove the fix with test calls recorded before-and-after so I can hear the improvement

You’ll have SSH access to the Linux server and remote GUI access to the Synway web panel. All work has to be performed live yet without interrupting production traffic for more than a few minutes at a time; I can schedule low-usage windows if deeper reboots or firmware upgrades are required.

Please tell me about similar noise-reduction jobs you’ve handled with Asterisk or GSM gateways and outline the first diagnostics you would run so I know we’re on the same wavelength.