Just an FYI........... Last week I replaced a water pump on a 2004 C-4500 LLY (I know wrong area to post but it shouldn't matter) and the only way you can get a pump from GM for this year vehicle is to get a pump kit which is just the pump with no housing. You have to swap over the housing, no biggie. Anyway, the new pump has narrower gear teeth than the original one. Of course I did not see this the first time (or the second time) and when I got the vehicle back together it had a gear rattle in the front of the engine much like a poorly shimmed PTO on the Allison transmission. I ended up reinstalling the old leaky original pump AS PER GM PARTAC so that the customer can use his truck until GM can figure out what the heck happened. I guess that they have several cases of this across the country and have no clue as to how the mix up started. Needles to say, I got pretty good at replacing the pump three times later. The purpose of this post is just to get you to take a look at your pump gear teeth and make sure that you don't end up chasing the same noise I had.