Jeannie

My Schnauzer is 6 years old. Every once in a while if he heard a loud noise outside (like a lawn mower or street cleaning), he would leave his usual spot and go into our walk-in closet. He now goes in there all the time for long amounts of time. Do you think he could be sick? He has also recently become very scared of kids. Our nephew (4 yrs old) came over and he hid behind me and didn't even want to take a treat from him. And the same thing happened with two neighbor kids around 5 and 7 years old. Any idea what all this is about?
We love our little guy and want to make sure he is ok.
Thanks,
Jeannie