I've never been lucky enough to fly in an Avanti, but the noise comes from the turbine exhaust being interrupted at 2000 RPM times 5 blades per revolution. Othe

I've never been lucky enough to fly in an Avanti, but the noise comes from the turbine exhaust being interrupted at 2000 RPM times 5 blades per revolution. Other pushers I've heard, such as a Skymaster and Long-EZ also make that noise so it may have more to do with the prop being in turbulent air. It's very distinctive.