Stimming has a variety of different functions, expressing feelings, calming, sensory feedback etc. The purpose behind his stims are extremely important. Is he stimming because he's anxious, stressed, happy, angry etc.
To give you some personal experience. Ds 14 has physical and vocal stims. When anxious he will aggressively hum the same nursery rhyme over and over. He will flap his arms and jump up and down repetitively when he's happy/excited. He will make the same sound over and over because it makes him feel calm and he enjoys the sensory feedback. His newer stim is tapping his fingers on glass windows with a certain rhythm, again for sensory feedback, he happens more when he's anxious.
We've had many stims over the years. Many many vocal stims, bouncing, sliding his foot on every grid he passes, stamping his feet. For ds they have changed significantly over the years, some disappear and others replace them. I've very much gotten used to them, they are just a part of him. They can actually be very useful in determining how he is feeling as he can't tell us verbally. Some can be redirected if they are causing damage or harming him. For example he will bounce on anything that gives him certain feedback. He has destroyed beds and sofas. I bought mattresses without springs, he no longer gets the same feedback so doesn't stim on them. He has been redirected to the trampoline and rebound cushion.
Your ds like mine is exceptionally limited communication wise. It's incredibly common for non verbal children to vocalise as a form of expression and sometimes communication, not all vocalisations will be stims. For ds he went through a screaming phase for about 2 years. This was him discovering his voice and enjoying the sensory feedback, it did my ear drums no favours. He would make different noises for many different reasons. Sometimes he would make the same noise over and over, one day I copied it (intensive interaction) and realised even though it was a stim that he enjoyed he wanted any form of communication with me. How often he did it decreased as he would seek me out to do it with him and then stop. His.vocal stimming and general noises have decreased as he's found alternative ways of communicating.
My advice would be to try and identify the functions of his stims and separate out vocalisations. He is essentially non verbal, that will cause frustration and he will find other ways to express himself. People used to say to me it must be really quiet in your house, couldn't be further from the truth. Non verbal or limited verbal certainly doesn't me silent! Sorry for the ramble, hope some of this helps.