mobile

Hi all,
I'm running out of ideas and could use another opinion please:
N6 running 5.0.2 (this is the second one incidentally, I sent the first one back for this same problem) - the phone will shutdown under certain circumstances. When this happens it does not restart, you have to press the power button to restart it. Mostly this happens when I use the Google Camera stock application to take a photo but only ever when the phone is not connected to WiFi. I have had it happen when I open the camera app as well (without taking a picture), if you put your ear to the upper speaker as soon as the camera app is opened you can here a cell location signal (similar to the sound you hear when you put your phone near a speaker) and then the phone turns off. I can stop this happening by using a third party camera app. I can also stop this happening if I disable Google location.
Yesterday I wiped the phone, signed in with my Gmail, and took 25 pictures, all OK. I then turned on Google Now, took one photo and the phone turned off. This is definitely something to do with location data but I don't understand why nobody else is experiencing this ? Maybe the phone is faulty but I'm going to have a hard to explaining that as I sent the last one back for the same reason.
Any suggestions are greatly appreciated.
Thanks,
Simon.