Yup it's the fan without Inlet guide vanes to support a bearing in front of the rotor. The vanes create a siren effect, while the open face blades with vastly different twist angles create a buzz.
I don't understand. It's the presence of inlet vanes that has an effect, or their absence, or what?
How come the L-1011 was noisier in cruise, despite the engineering changes?
Come to think of it, I don't really know what causes the classic high-pitched shriek of a jet engine. Is it just from the high-speed flow of air through the engine, or is it a siren effect from blades on compressors or turbines, or what? The shrieking sound always seems to be quite smooth compared to the buzz, although it has a certain edge to it that seems more audible at low engine speeds.
As for the white-noise roar that one hears especially on turbojets, I've always assumed that it simply comes from the high-speed exhaust (?), particularly since it seems to be really obvious on pure turbojets and aircraft in afterburner.