I have only found one brand, and it is not Kawasaki, does not have the rubber mated to it, and I think that is what causes the extra noise. I am like you , wish Kawasaki would make one. I have a 17 on my 2009 model, and I don't notice the extra noise, and honestly, have questioned the benefit. these are high RPM engines anyway, and love to run in the 7K range. Reducing the RPM's by about 400-500 really does not change much, just makes us feel better more than anything else.
40 years ago, it was guns, motorcycles, and wild women. today it is guns and wild motorcycles!!