B44 breaks out accelarating

[carborush]

here's a small prob riding my B44 :
when accelarating on loose sand the rear axle tends to break out a fair bit
going from one side to the other untill i loose the throttle and the grip returns
i already lowered the throttle curve on my esc to less nervous, but the prob stll remains
mabey I need to check the diff's or something ? anyone has any suggestions ?