Technically I don't know if we can call this cavitation since I always understood the term to refer to air coming out of suspension in water or the water "boiling" in the precense of very low pressure. In the case of boat propellors close to the water's surface the air can be sucked down to sit on the low pressure side of the prop and they call that cavitation. In the case of submarines or deeper surface props the prop driving too fast creates such a low pressure zone on the forward face that the water actually boils to a gas state even though cold. The problem goes away as the depth and pressure rises. I'll bow to anyone that can show me a different definition though.

But there is no doubt that props can suffer from bad separation bubbles ( which is a sort of cavitation I suppose) on their forward faces due to the low pressure and that shows up as that woosh sound.

I was involved in a bunch of static thrust testing of electric motors and props a few years back. We noticed that wooshing sound on many props. The current always took a big jump for the amount of thrust we got when that sound was present. It didn't take long to figure out that the blades were stalled and that was what caused the extra current demand. The stalling happened on various props and pitches but it was usually in the 8 to 10 inch pitch range. Bear in mind though that we were using airfoils on these props that had some undercamber to them and carefully shaped blades. The stock Zingers we used as a comparison showed stalling figures consistently in the 8 inch pitches and some in the 6 inch pitchs IIRC.

Anyway, the separation bubbles will dissappear as the Angle of Attack reduces. This reduction takes place automatically as the model gains speed. And that's why Paul's model audio is getting a bit quieter just before and after the woosh stops. He's launched it and the model is accelerating away from him and the microphone.