OK, I have been listening to mine, and assuming the car is powered up, with the handbrake on, then when I put it in gear (D or R) there is a short whirr from the brakes, then when I either pull away or let the brake off manually there is a long whirr as they release. That short whirr could be one of two things; either adding an extra bit of tension to resist the movement of the programmed 'creep' when you put it in gear, or some sort of 'pre-arming' ready for releasing.