Problem solved. Tigerpaw is an idiot. Helmet was never the problem. So...I take the 300 out with a different helmet and still hear the noise. I realize it must be my new textile Cortech jacket. Maybe the different layers of material or something. Maybe a vent is open. I continue to be dumb and press on with my ride, for hours. Stop for gas. Check all 100 zipper/vents, all closed. Continue to hear it, stop again. The light bulb in my head went off...all those zippers have real long pull strings...for gloved use. I spent ten minutes taking them off. was able to ride a few more hours, in quiet, but mad I didn't think of it earlier. Maybe I can dodge the rain today(Easter) and get some less frustrated seat time in.