FYI,
The foam for the CeeBailey is more than just a preventative for the whistle. I personally worked with CB to develop the foam "seat" or gasket. It also serves a mechanical function of spacing the inner surface of the wind screen away from the aluminum of the W-frame, and it provides better adhesion between the threaded rubber mounts and the shield surface.
Without the use of the rubber foam seat, you might (and I stress MIGHT) experience abrasion of the inner shield surface which could (and again I stress COULD) lead to stress cracks in the plastic shield itself. Of course, proper torque on the nylon mounting screws is equally important.
If you rarely run triple digits you will probably never experience any problem without the foam rubber seat. CB usually provides a foam seat to any previous purchasers of their screens who ask, and all new FJR screens ship with the foam gasket. They did a really nice job of designing the piece and the material is top-notch, just like their shields.
My strong advice, use the foam rubber seat. It's a bit unnerving to see a stress crack develop in your shield at 140 mph. Don't ask me how I know that!