I have a 2018 F150 and I am hearing a rumble under the hood when accelerating. It only last a couple of second and it is intermittent. It sounds like the waste gate either opening or closing but definitely not normal The dealership says if it doesn't hear it for them selves they can't do anything about. Of course it doesn't do it with them. I do have a couple of months left on warranty so I need to find out the problem ASAP. Any help would be greatly appreciated