I have a 2016 f250 with 6.2 with 16,000 miles. I noticed a rattling coming from the right side under the truck around the wheel well. I could not see anything obvious but I did notice on the rear facing vertical part at the bottom a spot of soot. There is definitely a hole near where it is seamed together. I think the rattling is inside the muffler.Has any one heard of any issues like this? This truck is in a lemon law case with ford over repeated problems with the AC not functioning properly. I am beginning to wonder about replacing this 250 with another one. This is the sixth new ford pickup I've had since 1986 and this 2016 has had more shop time than all of them put together.

 

It would not be unheard of by any mfg to have a seam failure where you are describing.......not common, but not unusual

 

Some mufflers are made with a small hole to the rear bottom to let condensation out.
Dave ----