Miele Dishwasher (8 years) G 2143 SCU very loud hum - loud enough to be heard around the house.

The hum is similar to that of a large electrical transformer, amplified by some resonance from the body of the dishwasher. The frequency is about 500 Hz (and lower)
It does not have the chattering sound of a water-hammer.

It happens just after the drain cycle.
It starts about 10 seconds into the water filling, and lasts for about a minute until the rinse cycle starts.
It happens in all the wash cycles.

The dishwasher seems to be working fine. The quality of the wash has not changed.
Just that this normally quiet dishwasher gets so noisy that it can be heard all over the house.
We've never ever added water-softening salt (our water quality is extremely good)

Any ideas about which component is generating this sound?
Is this a sign of an upcoming component failure? Or just something I have to learn to live with?

Thanks