My v6 5 speed mustang knocks while in reverse. Does anyone know what it could possibly be?

 

is it the guy in the truck letting you know he see's something back there. Think of it as oldSKOOL reverse sensing.

or could it be the entire car is pissed as it can go much faster going forward!

- sorry couldn't help it -

 

Fair enough. It drives wonderful going forward. I just hate being somewhere and I back up and everyone in the world is listening to my car clunk backwards.