Springs, Springs, Springs,
This may not be where your noise is coming from, but it was a problem with the 2006 workhorse.
I had the same problem at about 1k miles. Took it to workhorse facility. The service manager came out with a can of grease in a spray can.
Sprayed the springs where they connect to chassis.
Went back to campground, bought spray can with grease,,,,sprayed the holy moses out of those springs. NEVER a problem again.
But, when it first happened,,,scared the #$%^&* outta me.
I think this may be have been discussed here a year or so ago. A search may turn it up again.
Also, at the time, some folks as I recall either replaced plastic spring separators, or received some type of plastic wedge for the springs.