I thought some of you might find the web address that i am going to give you useful when choosing a pipe if you have to be concerned about sound as i do.You will see that there are not many pipes that come in at a legal level at least according to the test results given but it is a pretty good source for this topic that seems to be getting more attention lately.The address is(HTTP://WWW.OOHVA.ORG/).Once you get on this sight you will need to go to the (sound issues)section to find the information.