Rub occurs more often besides unbalance and misalignment. The current rub topic covers all types of rub. The Morton effect has similar vibration pattern as the Newkirk effect, though it occurs not that often. Parametric excitation here is referred to subharmonic behavior such as ½X vibration, due to either rub or bearing looseness. Since ½X is touched here, shaft crack manifested by 2X vibration is also discussed briefly.