I think the start up of the XKR sounds great and I just noticed that the exhaust flaps are vacuum operated. It kind of makes sense now as when I 1st start the car the exhaust note sounds great as the car runs in open loop for a minute or so. Also I hear the exhaust note change as the vacuum closes off the flap. When I go into dynamic mode the solenoid opens the vacuum line and triggers the flap. So I guess you could either pull the fuse for the solenoid or just remove and plug the vacuum line.