Sounds very much like you're hearing rusty discs to me, too. Never heard that on mine, though they were rusty when I got the car. Depending on your driving, you may be barely using the brakes as the regen does much of the braking for you, so the discs get barely used.
When I first got mine I was concerned about the amount of rust on the rear discs, due to it standing. I used the handbrake for a while when stopping to try to cut the disc back a little. It is not a top-hat type disc, so you're safe to use the handbrake to slow the car, which has the desired effect. The warning beeps at you but that's not important.
It is important to make sure there are no bands of rust appearing on the discs. Take a look. Over time these will exaggerate themselves because they wear back the pads which then increasingly do not touch the disc at those points. A few good, deep applications of the rear pads will help wear these away before they become a problem. My Grand Espace was like this when I got it a few years back, and much as I have tried to wear the rust back it has now taken over and needs new discs, which I'll have to do sometime this summer.
Due to changes in legislation (no more asbestos in the pads) the discs have to be made soft. So the pad and disc wear together, which can created self-perpetuating problems like pitting and rusting, but at least it has been dropped as an MoT failure point so long as the brakes are up to the required efficiency.