I have started to notice the fuel pump making a whirring sound, as the fuel lowers in the tank, the whirring gets louder. I've also noticed that the car shudders upon acceleration, like its not getting enough fuel. Whoever, as the engine warms up it runs fine. The car is a 1990 525i 5spd M20 engine. I don't think that the pump has ever been changed and the car has 285,000 k's. I also noticed that the inside of the tail pipes are a rusty colour and not the black or light gray that I normally see.