Compliments to the chef?

This is the sound Sully makes immediately after eating an entire can of cat food. I don't know what he's trying to express. I'm not sure if it's his version of loosening his belt and groaning, or if he is complaining about the food. If anyone reading this is an expert in cat psychology please enlighten me.

P.S. If you ever want to really freak out your cat, record it meowing and then play it back to them later.