I have a noisy Bosch Dishwasher?

Only recently did my Bosch dishwasher start making a horrible noise. When I turn the dishwasher on I hear it doing something like filling a tank or warming up water, this is very quiet BUT when it comes to spraying water on the dishes it makes almost like a grinding sound. I have gone through the cycle with all the racks empty just to rule out dishes interfering with the spray arm...........Help!