yeah very interesting might even be from the the s-bend from the turbo going to the underbody, once warm and on the slight incline + the torque on the driveline while in drive might shift the exhaust just enough to kiss the body, hopefully it is something able to be tightened or cut and re-bolted(which was my case) and not just a flaw in the exhaust making it too close. mate of mine who fitted exhausts for 5 years was saying whole sale they would get 15% off from buying an exhaust if they had a pipe bender on site so they could make slight adjustments without the need to send them back, as he said 95% of pre made exhaust were not a perfect fit.