Maybe not constantly scanning conversations within a mile, but maybe on purpose in order to escape Schanke's questioning and rambling. At that point Nick was still reluctant to work with a partner.

We encounter similar situations of acute hearing of a crime in “Killer Instinct“ (Nick hears something which is why he arrives on the scenes), “Crazy Love“ (Nick knows the address, but he hears the girl's shouts before he arrives on the scene) and “A more permanent hell“ (Nick hears Spark before arriving, both in the park and in Nat's apartment).