Noise in call between external caller and Agent

[PFCCWA]

Hello,

Has anyone experienced an issue where some kind of crackling noise can be heard between a caller and agent?
We are seeing this issue within our platform.
It is not occuring on every call, but frequently enough to be a problem.
Using..
Incoming calls through PSTN Lines.
Avaya Media Gateway.
SIP 8.1.0
RM 8.1.2
GVP 8.1.5
The noise cannot be heard when listening to call back in Verint.

Where can we investigate to determine root cause?
where is the cause of this issue likely to be - PSTN channels / Avaya MG / Genesys?

[cavagnaro]

PSTN lines are analog or digital?
QoS enabled?

[PFCCWA]

PSTN Lines are digital.
QoS is enabled - sip-ip-tos setting is 256 (not sure where this value has come from or how it is used).
Also noticed the option description states valid values are 0-255.

Thanks.

[cavagnaro]

You will have to do tests and capture SIP traffic with wireshark somewhere and try to isolate the issue.

Tests:
- Do a direct calling to agents, no GVP, lots of calls and see if you can reproduce the issue at least once, wireshark going
- Avoid also Avaya MG, call directly between SIP Server

BTW, which headsets are they using? Driver is ok?