Unable to post in the tech or general so I'll give it a shot here. Does any of your guys water pumps knock during the first few mins of warming up? Mines been replaced with new OEM last year since the one before was making a knock also. Even when i took out the old one there was no play in the bearing. There's no air in the system either, but when you put your hand on the bottom of the pump you can feel the knock coming from it.