a minimal pop sound will happen after you strongly deccelerate or after you cut off the bike after a ride. It happens rarely when I ride and when it does it doesn´t even bug me. This is one of the most dependable bikes you will get. I have put 15k miles on my bike and will put a lot more miles on it. This backfire issue that people make an issue of is nothing to me. Try the bike out and you will see what I mean.