Best thing to do is be informed:
Minnesota Statute 169.69 is the "muffler statute." Also see 169.693 for
motor vehicle noise. Hopefully the formatting of this message is ok.
169.69 Muffler.
Every motor vehicle shall at all times be equipped with a
muffler in good working order which blends the exhaust noise
into the overall vehicle noise and is in constant operation to
prevent excessive or unusual noise, and no person shall use a
muffler cutout, bypass, or similar device upon a motor vehicle
on a street or highway. The exhaust system shall not emit or
produce a sharp popping or crackling sound. Every motor vehicle
shall at all times be equipped with such parts and equipment so
arranged and kept in such state of repair as to prevent carbon
monoxide gas from entering the interior of the vehicle.
No person shall have for sale, sell or offer for sale or
use on any motor vehicle any muffler that fails to comply with
the specifications as required by the commissioner of public
safety.
169.693 Motor vehicle noise limits.
It is unlawful to operate a motor vehicle in violation of
motor vehicle noise rules adopted by the pollution control
agency.
Furthermore, be sure to read this, by the mn pollution control agency:
http://www.pca.state.mn.us/air/pubs/vtamp-fs.pdf