Vehicle is a 2006 Mazda MPV (new generation with the DISI Turbo engine and 6 speed auto).

The gear box has started to whine when under small to moderate load in 1st gear and 1st gear only. I've had it checked out by a transmission specialist, who said, apart from the whine there were no other obvious issues, but to keep an eye on it (particularly if it gets more noticable). The transmission fluid was also changed at the time and the sump magnet inspected.

My question is for someone out there who knows these transmissions inside-out. The whine is only ever happening in 1st, so my thought is that it must be caused by a mechanical movement that also only occurs when in 1st gear. My guess is that these 6 speed transmissions are WAY beyond just a simple single planetary gear set up, so can anyone shed some light on what this mechanical movement, unique to 1st gear, could be? Cheers.