I recently had to replace the rear transfer case seal on my 2002 Denali XL. right before the replacement when i hit 50 + mph i can hear a very distictive noise. As the mph increases so does the noise. So i thought once i replace the seal it would stop. i still have the noise at 50 + and I check the seal again for leaks and now the shaft can be moved around which is causing the seal not to seal tightly around the yoke.