How to increase your cars exhaust noise level for $0

If you are a rev head, and like to hear the exhaust, but find the factory setup too quiet, you can modify the exhaust to make it louder and more sporty sounding.
It is however, not easily reversible if you want some quiet or get sick of it.
I have a solution that costs $0 and is completely reversible! [emoji2]
How?
Simply open up the ski port in the rear seat!

Doesn't change much when I do that in my wagon :P

That's right, wagons are already open. This tweak is for sedans. On the R36 it's noticeable, which if I measure, should be a few decibels