At the Oregon Dunes National ORV Park there
is a sound limit for exhaust noise. While
visiting we noticed some 2-stroke motorcycles
sporting a 90-degree, copper water pipe fitting
for an exhaust extention. It was explained that
if the exhaust was directed at the ground, the
surface tended to break up the sound waves and
the bike was quieter.
I installed one on our Onan and now you can
stand next to it and hear the valve train
clicking.