rbdining

I have recently purchased a Dahua system components, comprising: 4off ipc-hdw3849hp-as-pv 8MP IP cameras and a DHI-NVR4104HS-P-4KS2 I am configuring the system on the bench before installation and I have come across a problem that has me confused. I am using the following setup . NVR connected to monitor via HDMI NVR connected to local network. A camera connected to NVR via CAT 5e cable (other cables on pigtail cable are not connected) I can view the camera from the web interface, DMSS iphone app and NVR display. The video feed seems OK and when I select the Talk function, I can talk through the camera speaker, but I can hear nothing apart from static noise from the camera microphone. I also do not hear anything when using the speaker icon (neither on nor off) I have turned on audio in the NVR. I have tried both the config tool, and the NVR interface. I have tried a second camera to confirm it was not a hardware fault. What am I doing wrong?