the trailer i was referring to is a California thing, they have mobile smog inspection stations, they use them to inspect random cars to be sure the state is staying within the c.a.r.b. guidlines, however the inspections are voluntary if you get flagged by an officer to pull into the inspection area. Other than that ya if your running headers and straight pipe and your exhaust note can be heard 5 blocks away and you happen to pass by a cop there going to pull you over. The only thing allowed here is short headers, if you have a pre-74 (I think, I forget the exact year they exempt) then you no longer have to get inspected and you can do pretty much whatever you want with it, even so you have to stay be below the xxxdecibal sound allowed.