When I have the engine at a high idle, It will randomly thump/bump and it is noticeable by just sitting in the truck. When it does it, The engine note also changes. Same at low idle but not as often. Sounds like its coming from the lower right side but with manual HVAC off which I'm having an issue with the a/c still on with controls on heat, It does it. No MIL or drivability issues at this time. I do have a strong exhaust smell when coming to a stop while driving and occasionally parked if windows open and no wind. Any ideas?