The pit area: up to and exceeding 130 decibels
The stands: 96 decibels
Inside a car during practice: 114 decibels
Racing: up to and exceeding 140 decibels
Here's what the NIOSH recommends as a remedy: "Crewmembers should be afforded the same hearing protection currently provided to drivers—that of custom-molded earplugs with built-in speakers. Workers at race tracks and spectators should also be made aware of the noise problem through education and informational campaigns."
However, as you can see from the comments on the NIOSH blog, telling them not to waste money on the survey (which was requested by the management of a professional racing team) and to "butt out," it remains to be seen if these recommendations are taken to heart.