N.D. Cent. Code § 39-27-08
Motorcycles must be equipped with an exhaust system incorporating a muffler or other mechanical device for the purpose of effectively reducing engine noise. Cutouts and bypasses in the exhaust system are prohibited. The system must be leakproof and all components must be securely attached to the vehicle and located so as not to interfere with the operation of the motorcycle. Shielding must be provided to prevent inadvertent contact with the exhaust system by the operator or passenger during normal operation. In addition, all motorcycles operating on streets and highways must meet the noise decibel limitations as established by the environmental protection agency. No person may sell, offer for sale, or install any noise suppressing system or device which will produce noise in excess of the maximum allowable decibel limitations of this section.
N.D.C.C. § 39-27-08