I remember the same thing happened to my old radeon 9000p. It made a loud squeal, and a few days later it stopped working altogether. Lucky for me, the card ran fine with the fan off, just on passive cooling, but I dont think a gf4600 is gonna survive without a fan. I'm not sure if oiling it is gonna help, (maybe temporarily), but it sounds like either get a new fan, or get ready to be shopping for a new card.