The shape, length, and diameter of the tubes in the intake manifold affect various aspects of engine response and performance. Changing any of those things doesn't make one manufacturer's engine design better or worse. It makes it different. Along with other factors, the intake design contributes to one engine having lots of low-end torque, ideal for getting a motor home going at a stop sign, and a different one having more high-end torque, like a highway police car that needs to go from 60 to 90 mph real quickly.
I first ran into the "manifold tuning valve", which I think is what you're referring to, on a '93 Dodge Intrepid. It effectively changes the the physical characteristics of the intake runners to change the engine's personality. It makes it develop more low-end torque at low speeds, and more high-end torque at higher speeds. You get the best of both worlds.
To try to isolate the cause of the whistle, pinch off, or unplug and block various vacuum hoses. I've never run into a noisy manifold tuning valve, ... Yet. That doesn't mean it can't happen. I would be more inclined to expect to find a leaking seal where the shaft goes into the intake manifold.
Sunday, November 9th, 2014 AT 12:19 AM