Mercedes E320 Oil?

We recently changed the oil in our 2000 Mercedes Benz E320 Wagon. But we noticed how when the car is around 1000 rpm, it makes a gargling/tapping noise. It makes this noise when you start the car and the needle goes up then back down to 1000 or when we accelerate lightly and then the needle hits 1000 again. The temperature of the car is usually above the 80 degree mark which seems a little unusual and the oil measurer computer that can be worked from the steering wheel says that we should "Reduce Oil Level" So how much should I drain from the car? Should we just keep driving it until the oil burns off?