What would cause voicemails to occasionally sound this bad?

Listen to this…


This is a sporadic problem that is happening on two servers.

One is a Trixbox 2.0 set-up with Asterisk 1.2, and the other is Trixbox 2.2 with Asterisk 1.4. This is pure VOIP - no TDM cards at all. I’m using Vitelity and both servers are really just used for incoming calls that get played an IVR and go to voicemail.

I initially thought the issue was due to the Trixbox 2.0 server being a VPS, or being related to network congestion, but my second server is a dedicated box in Denver in the same Data Center as the carriers.

The calls terminate at the server, so network congestion shouldn’t be in the picture. I have occasionally called into an incoming trunk and heard the announcement prompts be just as unintelligible, so it’s not just the voicemail recording playback that is garbled.

Vitelity doesn’t think it’s a carrier issue, they think it’s a transcoding issue.
I use ulaw and I save my voicemails as wav so there shouldn’t be transcoding.

As I said, this is a sporadic problem, and the calls are either pretty good or completely unintelligible. It occurs frequently enough to make me nervous and prevent me from rolling out.

Has anyone else run into this? Any suggestions?