Garbled audio issues with Multicast paging / RTP using PagePro

We are having an issue trying to set up Multicast Paging using the Page Pro module and are getting garbled audio to the phones.

  1. We are using the distro (10.13.66-17) FreePBX version and Asterisk 13.12.1
  2. We have verified the issues and behavior is the same on our 2 different production systems and our test system
  3. We verified that the RTP streams from the server and the Phones where both using ulaw
  4. We are able to successfully page from phone to phone
  5. We have tested the Network infrastructure and verified that multicast and RTP are working through the LAN switching and routing normally.
  6. We captured and analyzed packets during paging and found that we have the issue when using Paging Pro and when using the manual config

exten => 8998,1,Page(MulticastRTP/basic/

Pages would exhibit the issue and analysis showed multiple problems with the RTP stream including jitter and timing issues. (see images here and )

when using the manual config

exten => 8997,1,Dial(MulticastRTP/basic/

Everything worked and the streams looked good.(see here and )

Anyone have any suggestions on where to go from here?