Emmet claims to have "excellent hearing"—and while that's normally true for wombats and probably was true for him once, by this point his hearing is shot from spending decades around loud machinery without any ear protection. (And although he won't admit to being hard of hearing at least he's started taking measures to avoid losing two of his senses.)

Certainly nobody else has to consistently ask Sully to speak up. And he's not exactly the softest-spoken ferret in the world, although that could be because he spends his working hours around a hearing-impaired wombat and he just fails to adjust his volume downward after he leaves the Burrow. Maybe he'd have a smooth and dulcet voice otherwise.

Or maybe not.

Sully also likes to listen to music while he works sometimes. Usually while he's back in the workshop and Emmet is tinkering in the lab or in the office counting money or what have you. He's learned over the years just how loud he can crank up the volume without attracting the Boss's attention.

It's pretty loud. That wombat really must be losing his hearing... unless it's the case that he's standing in front of a security monitor, just watching. Perplexed. Mesmerized.

It's like a full body dry heave set to music.

Artwork by  FatsOutoftheBag