Guys, you are jumping to conclusions wayyyy out of line here. That sound is just the resonant frequency of your intake and exhaust systems together. If you ever watched your slides in your carbs when you run the bike without the air filter, you will notice the slides jumping up and down. This combined with the intake and exhaust valves and the length of the exhaust pipe makes for one specific frequency that your engine will make that sound. It is 100% normal, and happens so fast at another frequency higher up that you cant hear it around 10,000 RPM. At the lower RPM, 4-4.5k RPM it just sounds funny. At 10,000 it is what makes the bike feel like it is ready to jump away from you if you touch the throttle. This sound is totally independant from your jet kit or what PC map you are running. Each person's happens at just a little different RPM due to different densities of air and how restrictive your air filter is and what length your exhaust is. Hopefully this helps you out. :cheers