EPA noise regulations require that the following statements be included in the Owner's Manual.
EPA Regulations
TAMPERING WITH NOISE CONTROL SYSTEM PROHIBITED: Federal law prohibits the following acts or the causing thereof: (1) The removal or rendering inoperative by any person other than for purposes of maintenance, repair, or replacement of any device or element of design incorporated into any new vehicle for the purpose of noise control prior to its sale or delivery to the ultimate purchaser or while it is in use, or (2) the use of the vehicle after such device or element of design has been removed or rendered inoperative by any person.
AMONG THOSE ACTS PRESUMED TO CONSTITUTE TAMPERING ARE THE FOLLOWING:
  1. Replacing the muffler(s) and/or the entire exhaust system with parts not certified to be noise legal for street use.
  2. Removing or modifying the muffler internal baffles in any way.
  3. Replacing the air intake/cleaner assembly with one not certified to be noise legal for street use.
  4. Modifying the air intake/cleaner assembly in such a way as to make the vehicle no longer noise legal for street use.
Harley-Davidson recommends that any and all noise related maintenance be done by an authorized Harley-Davidson dealer using genuine Harley-Davidson parts.