It can be as loud as standing alongside a Boeing 767 at takeoff. And it’s about as irritating as having someone thumping on a bass drum in the back seat. Whether you call it wind throb or buffeting or just plain annoying, it happens when someone in the car opens a single window at speed and it stops when a second window rolls down.
The phenomenon that produces this noise is the Helmholtz Resonance, the same principle that makes a bottle hum when you blow over its open top. It’s the interaction of the gas in a container with a single orifice and the other gases that are, um, passing over that orifice. In this case, the container is the car. The interaction between the two masses of air produces vortexes that compress and decompress the air, producing the throbbing effect. Hermann von Helmholtz, the German physician and physicist who described this interaction, died in 1894 and was thus unavailable for comment.