Default Nexus 4 Crahs

Since i got my Nexus 4 I had a problem. The device crahs in irregular intervals. But it doesn't turn off completely. I just can't wake it up again. The notification led still keeps flashing (if I got a message in hangouts for example and didn't read it before the device "crashed"). I need to press and hold the power button till the device turns off. Then I need to reboot it. This happens not very often but it's very annoying and turns my nexus in a unreliable device. The first time it happened an alarm was set. I overslept...

This happens with stock 4.3 and 4.4 and also with CM

Things I've tried to solve the problem:

- factory reset and full wipe (multiple times)
- flashed complete firmware again (original google images for 4.3 and 4.4)
- flashed CM
- installed a custom kernel

Maybe it's a hardware problem???

What can I do?

actually I'm running CM10.2.1 + hells-core kernel