Maybe he can't hear well.
Either he feels you are not listening to him or he has a hearing issue or impediment.
It could be a hearing problem It could also be that he is a kid and kids take several years to learn to modulate their voices for normal indoor conversation. Check out his hearing and if that if OK, just keep reminding him when he needs to use his "indoor voice."
If you have taken him to Dr's and they say he is alright then he is fine. He is just being a typical kid.
Both of my kids are still loud at 6 and 8 and they don't quiet down unless they are reminded somehow. When they were younger I used to make them turn their own volume down by twisting their own ear gently like you would turn a volume knob down on a stereo. This worked for a while.
Now to remind them I will walk up to them and gently and repeatedly tap them on the hand or leg until I have their attention. This would be about as fast as you trying to keep the beat to a very fast song on the radio. I will urge that both of these things are GENTLE, lest someone think I am beating or abusing my kids.
Occasionally we have to result to talking louder than they are to get their attention, but the repeated promptings have made some headway. Get creative in finding a solution and good luck.
i had the same problem when i was younger.
i would recommend you to show him to an otologist or neuro-otologist. most of the time pediatricians don't have enough quality and knowledge to tell the difference between a chronic-asthmatic problem and an inner-ear disease. you may want to avoid an upper level semicircular canals problem..
sorry for being not-so-optimistic.
Keep it simple silly
Concern With Doctor about your son ear.Because when we listen loud then we also spoke loud