Unable to hear clips

i am using asterisk version 13.28.1. connected to the operator over sip.

I have successfully registered with my provider and getting incoming calls as well.

now issue is in hearing the audio at end user.

I can see the rtp packets are being sent to the MGW of operator, but he says call is silent.

I tried with both NAT Enable and disable. No firewall or selinux running on the machine.

Can anyone suggest on this??

I think some logs would be helpful. Also check your external media address settings in SIP configurations. That should be the same as your external firewall IP that your PBX uses for outbound traffic.