Always a good thing is new fluid, the filters are readily available on ebay, as is (usually - but it's expensive) the ATF+4. Just a thought for an experiment, firstly just simply don't touch the brakes going into drive from neutral. secondly chock the front wheels really well so you don't need to touch the brakes from neutral to drive, parked facing into a kerb perhaps, then see if it makes the noise. If it doesn't - it's brake related. Ours makes a light almost buzzing noise going into either drive or reverse, thought it was solenoid pack, so as I managed to get a new one from the States relatively cheaply I changed it along with fluid and filter. Made no ruddy difference!!!