Md. Code, Transportation § 22–609

(a) A person may not modify the exhaust system or any other noise abatement device of a motor vehicle driven or to be driven on any highway in this State in such a way that the noise emitted by the vehicle exceeds that emitted by the vehicle as originally manufactured.

(b) A person may not drive on any highway in this State a motor vehicle with an exhaust system or noise abatement device modified in a way prohibited by subsection (a) of this section.