MI HB5726

Establishes definitions for sound measurement standards including decibels (DBA), mufflers, exhaust systems, and OEM stock decibel levels for motor vehicles.

Sets noise limits for different vehicle types measured at 50 feet: heavy vehicles (8,500+ lbs) at 90 DBA on highways over 35 mph and 86 DBA on slower roads; motorcycles/mopeds at 86 DBA and 82 DBA respectively; other vehicles at 82 DBA and 76 DBA respectively.

Prohibits dealers from selling new vehicles exceeding maximum noise limits (83 DBA for heavy vehicles and motorcycles, 80 DBA for other vehicles) and prohibits individuals from operating vehicles with defective exhaust systems or noise-amplifying devices.

Prohibits motor vehicle repair facilities from modifying exhaust systems to produce noise exceeding OEM stock decibel levels, with violations subject to a $10,000 civil fine per violation.

Establishes penalties including $100 misdemeanor fines for dealer violations, civil infractions for operating non-compliant vehicles, and civil liability of at least $100 plus attorney fees for those who knowingly install excessive mufflers.