Low Speed Noise

[06 K1500 HD CCSB]

Anyone have any issues with a low speed noise which sounds like a possible drive line issue on their 2010 HD 2500 with the 6.0?? The noise sounds like it is coming from the middle of the truck and is noticeable at low speed especially when hitting bumps and turning. I did not notice this noise when the truck was new and I have about 600 miles on it know. I thought that the noise was the Nasta nerf bars that I installed about 300 miles ago but after a check yesterday and greasing all of the cab bolts at my dealer service managers suggestion the noise is still there?? I also checked to make sure none of the nerfs brackets are hitting metal on the frame so right know I'm needing any and all suggestions before I take it back to the dealer. When I explained the issue to my dealer they thought that when the frame of the truck is flexing the brackets/nerfs are creating the noise??? Thank you in advance for any help.