Netvanta UC Poor Quality Audio with NIC Teaming

I have one customer that uses Netvanta UC for their voicemail system. It runs on a virtual machine hosted on a Hyper-V cluster. That's a bit of an issue in itself because the software fails if the VM is migrated between hosts. To migrate it between hosts you need to reactivate it. Not cool.

For the past while, they've been having audio quality issues with this system and have investigated all points in the system, but none seemed to show any signs of an issue.

I'll let the customer describe it for you:

We have been plagued with garbled voicemail for a while now. Finally, we found some Adtran techs who took a hard look and found that when voicemail was hitting our NetvantaUC server sometimes (fairly often actually) up to 35% of the packets were out of order, causing a robotic and sometime impossible to understand recording. They also checked our PRI gateway and noted that there were no issues from the PRI (MTS) or leaving the gateway. Of course this left one switch in question, which we had already ruled out (no issues on the switch we could find).

This sort of left the VM host itself. I removed one nic from the team on Host 03 (where our NetvantaUC vm is hosted) and dedicated it to the NetvantaUC VM. For the past three days we have had no garbled voicemail and touch wood no phone issues at all (we had other phone issues daily, dropped calls, on hold and transfer occasionally not working etc).

So, it appears that there is some odd interaction between NIC teaming on Windows Server 2012 R2 and the Netvanta UC. At this point we're not sure if this is a general issue with VoIP software and NIC teaming or something specific to Netvanta UC.