So, we all thought that Nick’s superhuman hearing started when he became a zombie guy, but it seems that it started here in s02e15 Mr. Sandman. Maybe the changes that happened here were amplified by his zombification. 

Not that the writers have brought it up again since he got de-zombied, but it’s good for us fans to keep it in proper order.

I really respect that Nick tries to solve every case as a cop first and a Grimm second. It’d be a lot easier if he just was like “well, these wesen did this bad thing so now imma kill them.” but he doesn’t take the easy way out. Good on you, Nick. Good on you.