Engine upgrade or just exhaust?
 

I have an '07 Cooper Base that I've been wanting to modify so it's louder. As we know Mini's are decently quiet and while that is nice, I'm looking for a Subaru-like rumble. My question is how would I get that? Very new to the car world so this is a genuine question haha would I need to upgrade my engine or is it simply an exhaust related thing, if it's even possible? Thanks!