When I shift my ram into 4wd, everything locks in and 4wd is working, but as I go I get a hard pop from under my feet as if something is binding up and then popping loose again. I have replaced all u joints, the CV style bearing in the front shaft, the rear driveshaft, checked all my fluids....I assume a bad chain is possible, but wouldnt it pop all the time then? the case when turned by hand feels very smooth, the pooping seems to be worse the faster the truck goes....wondering if a broken mount somewhere could be the culprit...trying to eliminate all possibilities before I split the case, or hunt for a new one. has an NP231 case....anyone have any ideas?