mobile

Hi All,
Does anyone have any idea why the speaker on my Nexus 6 becomes active when the camera app is opened ?
So the reason I ask this is because, with Android, since KitKat, I have been plagued by phones that shut-down when I take a picture if my phone is not connected to WiFi. With my LG G3 I put this down to the phone itself and changed it for the Nexus 6 and the same thing happens with that. So, I figure it has to be an app I am using. So I have reset the N6 to factory, logged in with my Google account, set it up as a new phone and taken 20 pictures without an issue. I then enabled Google Now, took one picture and the phone shuts down.
I now have it to the point where if I open the camera app the speaker comes on very faintly and you can hear the cell broadcast sound, then the phone shuts down.
This only happens with the stock camera app by the way and only when there is no WiFi.
I am struggling to think why a phone that is reset, with no apps on it, is doing this..........and this is the second N6 I have had by the way (sent the last one back about a month ago for the same reason) :crying:
Maybe me resetting the phone from the settings menu is not good enough as it knows that it was originally paired with my Google account and will not let me proceed until I have entered my details.

Any ideas greatly appreciated. Apologies if there is a better section for this post. Thanks.

Simon.