M.M.
I work In a daycare and Children at this age hit all the time its easier for them then to use their words.If slamming on Drums helps him I would let him do it.Its like an outlet for his frustration just as we all have our outlets.If he hits other children just calmly take him aside and tell him that we cant hit our friends and if they are doing something he doesn't like he needs to use his words.If you repeat this every time they start to listen to you.I have gotten a lot of the children I work with to tell other children "not nice" "walk away" (these children are 17months to 2 years old. He will grow out of it as soon as he sees that using his words will git him further than hitting his friends. I hope this helps you out
Good luck