Welcome to the wonderfull world of the EPA....i've had 3 this year ....thats what ya get with a exhaust that has been tested at 89.7db, and a slightly deaf cop. The best place to get a EPA notice is from a booze bus!!
There's 2 types of EPA letter,
Letter 1 is just a noise test, where you take your car along to any of the licensed tester that are on the back of info notice that you recieved. (my personnel pick is Cheltenham ) The tester/exhaust shop bloke, will just test the db level of the car....the lucky number is <90db.
Letter 2, is a trip to the EPA testing centre in Macleod. Now the secrect for this test, is to take everything back to stock, as they test emissions, check under the bonnet, and a noise test. This is the letter you don't won't!!!!!!!!
Now letter 1 did cost $27, it has now gone up in price to $30-$35 (i can't rememebr )
Letter 2 cost's nothing, unless you fail. If you fail, you get a "greeny" sticker (it's not a sticker and looks the same as a canary, except green and usally falls of the windscreen after one warm day). The greeny is a notice that the car has failed a EPA test, and has 28 days to be fixed or be taken off the road. You can't sell the car with this sticker on...basically the same deal as a canary.
Hope that helps B)