yea, thats it, what happens is that when you open that screw, it changes the shape of the tunnel that lets air by, when you open throttle, a certain amount of air gets let through this opening. when the opening is just right, it passes over it just like a whistle making the noise. this is solved simply by changing the diamater and shape of the opening. Its just faulty engineering, not that anyone could have figured that out on the design board. glad to see its not just me who had the problem. It drove me nuts.