As you guys know, I'm enjoying the heck out of my cheap, ugly, dysfunctional rolling torture chamber of a B van.
One of the things that I like, that was a surprise, was how quiet it is. Considering the entire power train is under your feet, that is quite the surprise. I doubt there is any secret sauce or uber-design involved. I think they just used the normal automotive grade insulation in the cab floor and ceiling, and got lucky with their tire selection. I've yet to pull off the door cards to see what's in there. The Uconnect 5.0 head unit is certainly adequate to overpower any present noises - I certainly don't have any issues enjoying the XM. The dog gives me looks now and again - like he's saying "what?". Probably not that he can't hear me, but can't believe my crazy pontifications.
Dynamat has been used by automotive sound engineers for many years. Watch any car restoration show on TV and they'll be sticking dynamat all over the interior. It's fairly cheap now - you can buy it at Autozone and similar places - but it is heavy. So you have to balance how quiet you want it with how much weight you are willing to add. Just peel back your carpets and headliner and stick away. Another thing you can do is get quiet tires - research on tire rack and a little experimentation is needed to get the right tire for your van.
My new Honda Accord has a sound canceling technology included in the car stereo system. It cancels out the low frequency sounds from engine and tires. It's really effective. I wonder if something is available as an add-on module people could use in their vans?
My van has 2 stereo systems - the one in the cab (with xm) and an RV style sound system in the house. They are not joined together, which is a shame considering I'd like to enjoy the xm when parked. Any thoughts on how to get this sound in the house? I'm researching if I can do it thru bluetooth since both units support bluetooth streaming.