I found after long high-speed journeys with my roof down that my ears were, for a shortly while afterwards, being affected. So I decided to find out if driving with my roof and windows down could be damaging my hearing.
My decibel experiment.
Driving at 70mpg with the roof and windows down could damage my hearing after 8 hours and maybe sooner if also playing music. So now, on those very rare occasions when I driving long distances, I wear ear plugs as used by motor cyclists.