Take a look at the RD and cassette when in the 39/29. I suspect that the upper pulley is touching the sprocket through the chain. There should be more than a link (about 1") of free chain between the RD pulley and sprocket so they're isolated from each other and the RD pulley is leading the chain onto the sprocket.
Newer (since 2001) campy derailleurs don't have a "B" screw on the upper body to control the RD height, instead there are springs in both the upper and lower body and height is controlled by balancing the tension between them using the worm gear screw on the idler cage. Work by small changes until you see that you're heading in the right and adjust until you achieve pulley cassette clearance.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.