Abstract: Magnetic islands driven by the neoclassical tearing mode (NTM) present a major concern for the operation of present-day fusion devices as they can significantly decrease particle confinement and can lead to plasma termination. In low-torque DIII-D plasmas characterized by the ITER normalized parameter set and shape, disruptive NTMs are most commonly seeded by non-linear 3-wave coupling when the differential rotation between the q=1 and q=2 surfaces (Δf1,2) approaches zero. The rotation profile flattening is correlated with the growth of n>1 non-disruptive core islands. I will present integrated TRANSP-Kick analyses quantitatively characterizing how n>1 islands redistribute the fast ions in the plasma and modify torque profiles. The simulations presented here elucidate the experimentally observed non-linear relationship between Δf1,2 and the amplitudes of the n>1 modes, showing that the nonlinearity arises from phase-space resonance overlaps between fast ions and magnetic islands.