Since Visser Three had a human morph, in at least book 6, then why didn't he tend to repeat sounds and like food, just like Ax did? Since it isn't a host, he should be victim to a human's instinct for food, at least. The sounds were understandable since Hork-Bajir also make mouth sounds just like humans. But the food! Its a morph... he should go to the instincts too, right?
Also, if Visser Three tended to go crazy on food in human morph, should Tom be really suspicious when Ax in Jake morph tried to eat every edible (and inedible) thing in the house since Visser Three did it too?
It's not really an instinct. How many humans do you know that have such a craze for food? I mean sure, I like my food, but I'm not as mad as Ax about it. The impression I get from the series is that Ax's reaction was due to him not being used to having the sense of taste. I'd also imagine, although this is just a theory of mine, that a Yeerk would be better at controlling morph instincts than humans and Andalites can, especially if it's the first morph for both of them, as a Yeerk is used to being in and controlling the body and instincts of other species.
A Yeerk is very used to controlling their excitement about new senses: they do it whenever they're in a host. Taste is no different. Also, V3 would have experienced taste in Hork-Bajir: bark may not taste good to us, but that doesn't mean it doesn't to a Hork-Bajir.
And, as others have pointed out, V3 may have never eaten in human morph. You also have to remember that Ax was a pretty young Andalite when he first started the series, with little experience of morphing. Even Alloran on his own would, I imagine, be able to control the joy of taste better than Ax could at first.