Today I took my 2015 Yukon Xl for a drive with the service manager. In the last week it has received the PIT5318C roof bow work and it received the PIT5404 exhaust system replacement. The service manager commented that the buffeting did not really improve until after the exhaust change. The difference in the exhaust is the valve for V4 used to be behind the muffler and with the revision it was moved to before the muffler. I guess this is logical since that would help deal with the change in tone when you go into V4 mode. There is still a vibration that will be measured with the PICO (sp?) meter to help isolate, but he acknowledged its presence and wants to use the equipment to hone in on the source. I have had my rear tires RFB 2X since October.