04 drivetrain noise
 

I have a 04 f150 crewcab 4x4 lariate with a 5.4. 115K miles. There is a very loud noise that sounds like it is coming from under the cab that sounds like a log chain being wrapped around drive shaft or a chain being drug over a piece of sheet metal.

It's only made the noise on two occasions. The first time was this summer while pulling a 3000 lb camper. I was pulling it about 60 mph and when I came to a stop it quit. Once I got going again (less than 5 mph) it did it again, then a clunk I could feel, then it quit and ran fine.

I took it to a shop and they didn't find anything wrong.

It did it again this week under no load and at about 20 mph. It quit and is running fine now.

Any ideas?