Why Does Our Mini Schnauzer Make Popping Sounds When We Ask Him If He Wants To Go For A Walk?

This is a behavioral problem, not medical. Many dogs will make various noises, and it's possible he's just voicing his happiness. Some dogs are known to be more vocal than others, and this does not seem indicative of any diseases. It's possible he just likes the feeling of popping air in his mouth and does it to show pleasure. As long as your dog is able to bark normally when he wants to, I see no reason to be worried about his health.

If you want him to stop, then try distracting him when you go for a walk, and he will not have the time to make any noises. Do take him to a vet if he stops making any noises, seems to be in pain, or shows any other symptoms of being sick.