[cisco-voip] Poor voice quality for cue AA announcement

[Ki Wi]

It's a remote site, 28xx voice gateway with cue connected back to a cucm cluster via cti (typical cucm-cue setup).

However, there's a intermittent issue with the voice quality for announcement from cue. 

Basically customer call in via analog line, it will be routed to AA in local cue. Signaling wise it will goes to cucm cluster and hit the cti port.

How do I troubleshoot in such situation? I have ensured that there's no transcoder triggered along the way.