SFR can usually provide sound readings for your car on request. At PIR, one can just watch the city-provided meter on their website.
Did your car bitten by the Thunderhill sound bug on Sunday morning at the Thunderhill Majors? My car magically grew 5db+ louder overnight from Saturday. I was reminded of being at Laguna Seca. Doing a sound check with simple turnaways didn't make enough of a change afterward.
One of the GT1 guys paddocked next to me recommended some nasty "Car Chemistry muffler inserts" that the T-Hill shop was selling. For higher-power engines they probably don't hurt too much but they served their purpose for me (and others) sound-wise for my 2.7 flat-6. They are easy enough to pound in and remove; they are in inexpensive to keep in the trailer. Luckily we didn't see the meatball during the afternoon races after adding them. My ears couldn't tell the difference in-car, FWIW.
