You hear it, when you didn't have the sport exhaust. With sport exhaust even without pressing the button you don't notice it.

I had them on my 981 S without sport exhaust and it was noticeable with full throttle open, on my GTS it didn't hear any difference. But I didn't drive the car directly before and after, because of bad weather.
 


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daily: BMW 430d
for fun: Porsche Boxster GTS