Mine had a RATTLE for a few minutes on a COLD start. Went away after warmed up. As the water pump got worse... it took longer for the RATTLE to go away. The rattle had a slight GRINDING noise to it. Best not to let it go too long if you have this noise :shock:
Most WP's have a weep hole that will begin to leak coolant once the bearing seals weaken. So a spot of antifreeze on the ground coming from the block is generally the first sign. Once the bearings get washed with coolant, they start to die and that is when you get the grinding or loose marble sounds. You really need to get the WP replaced soon or you risk having the worn bearings seize the shaft. Then the shaft seizes bad stuff happens!