I have an open downpipe on my supra and it sounds like a goddamn demon. It rattles your teeth when cruising on the interstate and I have to blast my 2000watt stereo to even hear ANY music. Win will testify For reference, this is just putting along in a parking lot:
http://www.tlink.net/parking.wmv

But i've never been pulled over or harrassed about it, even though there's clearly no exhaust in sight on the car!