my 07 xkr came with a upgrade rear box lovely deep roar, it has dissapered, still good rummble but not as deep when power squirt. Took out fuse f19 , no difference. Would give it an odd quick trottle blast when parked, wud i had blow baffles in box.
Was talking to a guy with a 911 and his box noise dissapeared completely to just a slight noise, he was getting a new system.

 

Fuse 19 is for the circuit that controls the active exhaust system on XKRs. If you disconnect it, all four exhaust pipes will be open all the time. This is a nice trick for 4.2L (2007-2009) XKRs since they do not have a dynamic mode, which will do the same thing for the exhaust.

I bet the guy with the 911 has an active exhaust with broken exhaust valve actuators/mechanism!

 

Or he is going deaf!

 

box is straight forward fittment, connects straight into smaller middle rear boxes, wud my exhaust valves be stuck