Bill,
I have a 2000 3500 with Westin Nerf Bars and the exact problem as yours. I would hear a creaking/popping sound when applying the brakes or going around a corner. The tech at Karl Klement Dodge and I both thought it was a rear brake problem. After we just about took the truck apart, we finally decided is was the mounting bracket on the left rear nerf bar. He tightened up the mounting bolt and the noise went away. I drove the 18 miles home the back way on country roads for a test and the sound was worse by the time I got home.
I took the mounting bracket off and drove down the road--no noise. I later decided to swap sides with the rear mounting brackets and guess what--no more of the noise. I have been about 7,000 miles now and the noise hasn't returned.
I would swap sides with your rear mounting brakcets and see if that fixes your problem. Also don't torque the mounting bolt quite as tight as called for in the service manual. I think it calls for about 50-60 lbs. ft. , but I torqued them to 35. Good luck!!!
Bill
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Y2K 3500QC, 6 Speed, 4. 10, SLT+, Camper & Tow Pkg. , Westin Chrome Nerf Bars, Mopar Flaps, Reese 20K Hitch, V-A CPC, EGT & Boost Gauges, RPM 45 Gallon Aux. Fuel Tank, Highway Products 5th Wheel Toolbox, ECM Controlled PacBrake, Painless Wiring Kit, Mag-Hytec Diff. Cover, 80% Towing Hitchhiker II 31', 2 slideouts, 19,750 GCW