I understand straight cut gears whine. But wh does the sound come from the intake and not the other end of the SC where the gears are? If I rev it by hand under the hood, it clearly comes from the intake.

Well, the gears are pressed onto the rotor shafts themselves, but isolated by the coupler in the nosedrive. That sound (vibration) is transmitted to the rotors themselves, and the only OPENING to the outside world is the intake end. With the baffling of the stock airbox gone, that sound can be transmitted more effectively.

My theory anyway.

[in best infomercial voice]
Well, I'm skeptical, Bill.
[/voice]

Opened intake - less noise baffeling. I'm clear on that point.

Maybe a combo of both gears and harmonics? Maybe...