I agree. A good trainer will help you figure out why the dog is growling.
Personally, I would not be correcting the growl. The growl is communication. If you tell the dog is not allowed to growl then you give it no choice but to react. Many may disagree with this advice.
I would also be crating him at night. Because we don't know the root if the issue, he should not be allowed in your bedroom. Or on the bed or furniture. Your son should take an active role in his training as well. Teenagers are big, gangly, hyper, their voices are weird, their hormones are raging, they can be quiet unsettling to a dog.
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