Turn down the volume?
Seriously, it's not like the Sienna has external speakers or anything. Any audio heard outside the car is originating inside the car. I haven't actually checked in our van, but in my wife's RAV4, I know if she's on the phone inside the car and I'm standing outside, next to it, I can hear the conversation clearly. But, I can only hear it if I'm within a few feet of the car- exactly the same as you would hear if 2 people in the car were having a normal (or perhaps slightly loud) conversation. If your son says he can hear it up the street, either: a) he has super-human hearing, b) he's messing with you, c) one of your internal speakers has broken free of it's mounting and somehow reoriented itself so it's pointing out instead of in.
First thing I'd do is put someone else in the car and have them make a call while you walk around outside and see how bad it really is. If you can only hear it within a few feet, that's perfectly normal.
2015 Sienna SE - Predawn Gray Mica
Last edited by tweak4; 12-13-2016 at 10:20 AM.