The STI provides a distinctive exhaust note due to their motor.
There are a few exhaust systems out in the market now from aftermarket to Kia Canada's performance axle-back exhaust (Kia part no. 99997 921M01).
Kia's exhaust has a really nice deep rumble to it and a sexy burble sound when you let off the throttle.
There are 7 videos (incl. the stock sound for comparison) of different scenarios so you can get a idea of the sound you hear during everyday driving. Search for 'Koup SXR'
The first few pages of my build thread shows you what's involded on the installation side of the Kia exhaust.
you can get it.. however that requires you to get ancustom un-equal length header made ( this is what contributes to the sound that sti's and subarus have. look up sti's with equal length manifolds they dont sound much different then a "regular" car)
and really its not worth it.. IMO the kia sounds great for a stock car