[Serusers] 2 SER network using 1 PSTN provider

Hi all... Just came across a problem with running 2 individual SER for 2 separate network. They both work fine independently, yet I have subscribed for PSTN landing of calls for only 1 SER server (IP restrictions). Now, for my second SER server, I have forwarded calls to the first server (much like pointing a call to it using "if uri=~" command........ and of course, in the trusted table of SER 1, I have placed the IP of the SER 2. Now... the call goes through and the can be landed, yet the PSTN user can not hear anything while the IP Phone user can hear perfectly from the PSTN user. The 2 SER servers are setup based on onsip.org with mediaproxy configuration. Everything works fine, except for this 1 way audio problem. Could some please point me to the right direction to where to solve this?!?! By the way, if my IP phone were to use a REAL IP on SER 2 and try to land calls via SER 1, everything works perfectly!!! There will be 2 way audio. So I would imagine this has something to do with mediaproxy or NAT issues. PLEASE HELP!! :>