How to keep my dog from whining/barking/howling when I leave?

My dog is 9 months old and he cries/whines/barks/howls nonstop when I leave my apartment. During the summer, he stayed with me at my parents' house and he was happy because there were 2 other dogs that he could play with. Now that I've moved back for college and am living in an apartment, he goes crazy when... show more My dog is 9 months old and he cries/whines/barks/howls nonstop when I leave my apartment. During the summer, he stayed with me at my parents' house and he was happy because there were 2 other dogs that he could play with. Now that I've moved back for college and am living in an apartment, he goes crazy when I leave the apartment to go for school. The neighbors have been kind enough not to call the apartment management, but they did leave notes on my door asking me to please quiet my dog. I've tried leaving him toys that he likes, giving him those raw hide things to munch on, music, TV, and he has enough food and water. I leave him in the living room so he has enough room to roam around. I don't know what else to try in order to get him to quiet down. My neighbors will surely call the management if this keeps up and I don't want to be a bother to my neighbors. How can I stop this behavior quickly and efficiently?

Thank you!
Update: He is a Miniature Schnauzer. I know that breed tends to have some problems with barking, but this is quite excessive!
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