One word, preload... very easy to destroy one if it isn't shimmed properly. If it is overloaded it will cause the bearings to burn up and cause all sorts of issues, and if it is underloaded and has some play to it, well, you get the picture. This has to be MEASURED and not just guessed when any diffs are installed, even stock for stock. Each diff is shimmed to its own case. If the diff was properly installed, then maybe a manufacture defect? Who knows?