Well, if all else fails you can duct tape some deer whistles to it.

What size are the holes you drilled in the aluminum? could you stick some drinking straws in them with the ends cut at an angle? Let the straw protrude from the flywheel so it can catch air? Trying various angles to see if any work? There may be a boundary layer of slower moving air near the flywheel. The flywheel may be "dragging" the air with it. Not much on fluid dynamics here, (yes, air is apparently a fluid

) but I know it can happen when an object like an airplane moves through air.
Though I have looked at some whistling arrowheads and deer whistle designs. You may be able to incorporate the arrowhead design into the flywheel.
It might also be cheaper and easier to make the prototypes out of wood instead of metal. Just from looking at the arrowheads you might try drilling the holes at about 45 degrees off center of the flywheel center.