Drive line noise mystery? Solved

[Rockhwy]

I think you are right the spring that is on your front axle should be on the rear axle. You can Google leaf spring for peterbilt low air leaf and diagrams of suspension will come up from various web sites. You can also Google peterbilt low air leaf rear cut off and salvage yards have them for sale with pictures I looked at some and they all looked like spring with the bigger arch goes on rear axle if you had all 4 springs replaced looks like yours are opposite. I had a peterbilt with low air but was old style yours is new style like 2006 and newer Kenworth also uses your style I have peterbilt flex air kenworth also uses this suspension