'friend of mine had this (with his cat, not him personally). Vet said to stop mashing the food, just slide it out the tin/ sachet. Means they have to eat it slower. As mentioned, wolfing the food and taking in air is a big prob.
Ours are pretty much on Royal Canin dry (male) as advised by the vet, to keep weight down. They don't seem to whiff at all.