welcome to Perth-WRX.
Plenty of info in the search function of this forum.
If you install a full Turbo Back Exhaust (
TBE), you will need a re-tune. If you just want some noise without having to do a tune, then you can install a Cat Back (
CBE) and run that, although your fuel economy may go down a little.
Welcome to the world of WRX's
Enjoy