OK, since I can reproduce this easily I have to ask if anyone else is experiencing it:

When driving at 30+MPH, if I put up all the windows in my TCH except one of the rear windows, I get a very rapid ongoing pulsation of air pressure inside the car, I'm talking repeated overpressure, to the point where it's actually painful on the ears. It stops when the last window is put up, or if I open one of the front windows. I learned very quickly that if all the windows in the car are open, I close the rear ones first. Has anyone else noticed this, and if so, figured out what causes it?

I can tell you it is NOT a wheel vibration. It's some aerodynamic effect and grows more pronounced (and painful) at higher speeds.

(It's actually an '09!)

I've had that in every car I've ever owned. It's nothing special to the TCH. AS the air passes by the outside of the rear windows it sets up a resonance inside the car, giving the loud throbbing. It diminishes dramatically by carcking one of the front windows slightly, allowing a real air flow through the car.

--My hybrid came home!--
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Randy

I had this problem with my previous car, a Toyota Rav4. It is as rmorrow describes, a resonance of air displacement.

Resonance is the word I was looking for and couldn't remember, thanks. That's exactly it. It's odd to me, as I've never experienced this with any other car.

(It's actually an '09!)

Yup, me too. If I roll my window down I always take another window down at least just a crack. On my Sienna (and the two GM minivans before), I always opened the rear quarter windows to eliminate this situation as well. I used to have an old Cavalier with manual windows. Fortunately it was small enough that I could lean over and crack the passenger window, or reach behind to crack open the backseat window whenever I wanted to have the driver's window down all the way. The guy that bought it from me put those rain guards on so he could have the windows open a crack all the time.

Two climate control systems, one inside and the other at the tailpipe.

2007 Camry Hybrid (in service June 2006)
2004 Sienna (in service May 2003)

I get the same issue with the sunroof open and a (I forget exactly which) combination of other windows being open or closed at the same time. Closing the sunroof a tad fixes it.

Removing the reverse flow "flutter" valve from the exhauster (usually in the bottom of one or both rear quarter panels) port will help somewhat.