the faulty one can some times stop working after a few minutes and then there's times when it wont go above 4ghs and it will beep at times even tho I'm sure the u3s don't have a speaker this is why I think it is faulty and will be looking for an exchange.
Ok that you would be right on second one sounding fault if it only reaches 4ghs and you tried different things to operate it and still happens. That is not normal so getting a refund your right would be proper.
But on your one running over a week that is luck. Zombies normally hit U3's much more often then that, the more you have the more you see it. When I had 3 I was resting multiple times a day zombies are just that common. The R1 with CrazyGuys firmware saved all that though.