Noise Limits - Important!!
Noise limits are a sad but necessary evil, they keep local residents happy whilst allowing the circuits to operate. The closer the circuit to local residents the tougher the limit. Fact is without them track days would be few and far between.
Most circuits can still run a limited number of events, including track days, at elevated noise levels and can have different limits for each layout or even days of the week.
With all these variables you need to check the noise limit at every event before you sign up. If you're over the limit you won't be allowed on circuit and you won't get your money back. It's the worst possible outcome and to be avoided at all costs. If in doubt get your car properly tested, there are no exceptions, and avoid the stress!
How can I reduce the noise?
You can buy noise reducing baffles to put on the end of your exhaust but in reality it's a high risk strategy and you're missing the point. For most cars the problem is the choice of upgraded exhaust system and/or the removal of the Catalytic converter. Choose wisely and you'll get the performance improvement without overdoing the noise so you can take your car on track.
How can I test my own Vehicle?
If you've modified your exhaust and the change in noise level is apparent you could buy a fairly cheap dB Meter or even get an app on your phone to give you a reading. However, for an accurate reading it's better to go to a garage or environmental company or even a local race circuit with professional, calibrated equipment.
What if my car is just noisy?
Some cars can be right on the limit with factory specification. Once you know the noise level of your car just stick to events with suitable noise limits.
Static Noise Test
Static Noise Testing Specifications (derived from MSA Regulations)
Drive-by Noise Test
The static test is very specific and doesn't guarantee compliance on the circuit. To monitor the actual noise levels around the circuit there will be microphones at strategic locations, usually near the start line and almost always on straights in areas of high revs. The drive-by limit will be lower but the microphone will also be some 10 Metres away. It's rare to fail the drive-by having passed the static test but it does happen. Thankfully it's not too difficult to comply with the drive-by just by changing up early or backing off slightly in the vicinity of the microphone.