The truth is that most dogs that have pent up energy, due to insufficient exercise, do have a tendency to become destructive and create their own form of "entertainment". This applies to puppies as well and teething contributes to the need to chew. A dog's back molars should come in by 7 months of age.
Miniature Schnauzers are a particularly energetic, lively breed. They are intelligent, playful, strong-willed and have a tendency to become destructive and develop behavioral issues without daily exercise. A firm "pack leader" is essential and daily walks are the ideal activity to drain excess energy and bond with their owner. Proper walks, training the dog to walk by your side, (never ahead of you), will teach the dog you are in control and he/she is to be submissive.
Miniature Schnauzers were bred to hunt vermin and will instinctively find objects to "capture" and "shake dead". (Even my toys poodles do this, by the way.) Provide a variety of acceptable toys and chews for you dog. Playing fetch or simply throwing the toys will trigger your dog's innate drive to catch prey and "kill" the toy. Objects that are off limits should be kept away from the dog if possible and/or try spraying them with a commercial pet bitters product. "Fooey" is alcohol-free and is non-toxic. Another option is to spray forbidden items with a strong vinegar solution, (test for color fastness, as needed).
If your dog has a tendency to misbehave when you are sleeping or away from home, he/she should be crated or confined to a small area. Should he be permitted to have opportunities to be destructive while unsupervised, the behavior will become more ingrained.
Changing the dogs routine to provide ample exercise and mental stimulation and acceptable toys can be helpful to improve your dog's behavior. Best wishes.