Clark's superhearing isn't always on?

there are inconsistencies everywhere, truth be told, he should never get tagged ever but he does because it apparently enhances the story...

besides he's still young, one can say his powers are still manifesting themselves, especially the ones he's gained during the show...

one can say he needs to focus to activate them and that's why they aren't on all the time.

 

And given the instances you site about the loft and the knife you could also say he was lost in thought.

I mean think about when you get lost in a movie or book and people sneek up on you when normally you'd hear them.

 

I've always thought Clark's hearing wasnt a passive power like his invulnerability, I thought it was something he had to actively try to use like his x-ray or heat visions. That would at least make the "sneak ups" more plausible.

 

It definately has to be, or else every sound within a thousand mile would clog Clarks head.

 

i was more upset that Clark let the Phantom Zone Bracelet fly pass him