A new mechanism whereby Neoclassical Tearing Modes (NTMs) can be triggered through toroidal mode coupling to a frequency sweeping fishbone instability driven by energetic particles is proposed. The novel physical picture is the presence, prior to the seeding process, of a "pre-NTM" magnetic island of relatively small width, rotating at a frequency within the diamagnetic drift band, so that the polarization current is stabilizing. The main effect of the fishbone is to exert an electromagnetic torque that changes this frequency so that the polarization current becomes destabilizing, driving the island above the critical seed island width, in which case NTM growth ensues.