Have you followed this:
https://doc.pfsense.org/index.php/PBX_VoIP_NAT_How-to
and this:
https://doc.pfsense.org/index.php/VoIP_Configuration
?
Audio problem, especially one way, are frequently caused by improperly configured NAT but the problem should be consistent I believe so I would not be surprised the problem is once again with snort…
Good luck and have a nice day!
Nick