Recently I am having similar issue, mines a 2006 model, 125,000km on the odometer and on acceleration I hear like a raspy sound, its only when in drive and when accelerating gently or tapping the acceleator. Once it revs over say 2000rpm, it dissapears.
I have recently changed my oil from 5w30 to 10w40 and the raspy noise is still there. Its never there when cruising along or travelling at higher speeds (higher revs).
Have replaced air filter, oil, checked the transmission fluid etc, all seem fine.
Any help or ideas would be appreciated...