Been having a weird sound coming from underneath the truck since a accident. Ford has no idea what it could be. They have already replaced the Cat, oil pan, turbo and checked all heat shields with no luck. It only happens at cold start up and last about a mile or two. Has anyone else had this issue and figured it out?

2017 F150 XLT Twin Turbo Limited

 

I've ran into a similar problem a few times with f-150s. there is a band on the y pipe coming off of the bank on the drivers side. it rattles only at a certain RPM. it holds on the little shield at the y pipe where the two exhaust pipes are about to join

 

Thanks for sharing that tip.