They idle mellow, but if you hammer it they bark. Not the loudest gl***pack out there. Do a search, there are dozens of threads on Smithy's (BTW, it's spelled Smithy for your search).
Here's my car with smithy's on it. The quality isn't that great. But you can still hear the car. http://www.youtube.com/watch?v=VNZvspxJyk0
I have a pair of the shortest ones they offer behind a pretty much stock 283 with 2 inch pipe. They sound great but they are fairly quiet.
They are over-priced and just too quiet. Come to think of it my ex-wife was overpriced and (O/Rated) but never as quiet as ****ty's
I recently put a pair of Thrush 2" 17" long gl***packs on a car with a 390 4 speed.... I put them as close as possible to the front of car and ran them straight with no bends under the axle out the back..... I had problems getting them hung right and gave up and took it to an exhaust shop and had it done right over the axle... They moved them before the rear wheels... It sounds great and raps nice when wound out.... I had Smithy's on a similar car but with an auto... The Thrushes sound better and are cheaper.