As above, probably wrong time wrong place. If you're innocent and polite to the police, they'll show you the same respect back. It's unfortunate that sometimes a few idiots ruin it for the rest of us.
Personally, I have never been pulled over by a highway patrol, though I have been randomly pulled over by a single cop whom had set up his own RBT station on a rural road around Glenorie, NSW. After breathalyzing me, he walked around the rear of my car and stared at it for a few seconds (which felt like a whole heap longer!), came back to the driver's window and questioned it's loudness: "It sounds a bit loud, don't you think mate?"
"mmm yeah maybe - it's not that loud though?"
"Okay, off you go.."
I've been through a few RBT stations as well where the police have had a good look at the outside of the car, but they've never questioned the volume of the exhaust or given me a hard time. I figure, RBT stations are really out there to catch drunk drivers - not to write up defect notices?
For the record, I am not quite sure what exhaust is in the car. Some kind of custom 3" though.
Does anyone know how many decibels the legal limit is for exhausts in NSW?