Over the past few weeks, I've been hearing a whiny, grating, whirring sound coming from the engine upon start-up. It would go away after a couple of minutes as the car began to warm up. Took to local MB tech and left overnight for cold start. He put stethascope(?) to various parts and said it's the waterpump. I didn't have the $600 at the time, so I've been stalling. Not much change until recently. As the weather is getting warmer, and my garage temp climbed from about 55 to 60, I don't hear the sound any more at all. Pump still seems to be working (driving temps OK and no coolant everywhere!). Any ideas?