[Q] Randomly dropping calls

Hey guys !

I have a problem with my Nexus 6. I'm running stock 5.1.1 unrooted with latest update(48M) and keep getting dropped calls (I only use 3g). It doesn't happen all the time, today I got 4 dropped calls. I'm not quite sure what's the problem. I have the phone for 1 week and I'm not sure if that's a hardware or software problem. (I also had Chroma installed and had the same problem)

Are you guys facing this issue?
Is there any thing I can do?

Thanks !