Loud vehicles are governed by Wisconsin state law, not a county ordinance. Wis. Stat. 347.39 requires an adequate muffler that prevents excessive or unusual noise and bans exhaust modifications that amplify sound. County sheriff and municipal police enforce it on all roads.
The Waukesha County Code has no vehicle-noise chapter; instead, Wisconsin's equipment statute applies statewide. Wis. Stat. 347.39(1) requires every registered motor vehicle to have an adequate muffler 'in constant operation and properly maintained to prevent any excessive or unusual noise.' Section 347.39(2) prohibits cutouts, bypasses and any exhaust modification that amplifies noise above the original muffler. This covers loud cars, motorcycles and modified exhausts on Waukesha County highways and municipal streets alike. Separately, unreasonably loud stereo or revving that provokes a disturbance can be cited as disorderly conduct under Wis. Stat. 947.01.
Loud/defective-muffler forfeitures run roughly $98–$124 with 0 demerit points under Wis. Stat. 347.39; disorderly conduct (947.01) is a Class B misdemeanor for disturbances.
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