We are getting one way audio issues with some softphones and grandstream phones behind nat registerd to our freeswitch server. 

Here is scenario: 
Grandstream call any extensions (one way audio) 
Any extension call Grandstream ( Audio works just fine)

We have tried multiple softphones and the result is same. 

Everything was working fine with 1.4.18 and 1.6.2. We were having DTMF issue with 1.6.2, upgraded to 1.6.5 and now one way audio issue started with an upgrade to freeswitch. 

Any help or hint will be much appreciated. 

Thank you,