Successful interstellar venture depends on the development of propellantless propulsion with a thrust-to-power ratio much greater than a photon rocket and without the limitations of solar sails. Claims of μN thrust for Woodward's MEGA Drive, along with predicted mass fluctuations as a consequence of the Mach-Effect have initiated a few decades of table-top experiments seeking to observe variable mass and using it to generate significant propellantless thrust efficiency. However, using different thrust balances with increasing measurement sensitivity to characterize these effects resulted in a decrease in the claimed effect's magnitude. Large second harmonics begin to appear in the pre-stressed piezoelectric stack's integrated strain gauge signal, showing the vibration present at system resonances, as well as significant nonlinearity. Observation of the balance beam's oscillations reveal sub-harmonic vibration coupling and amplified vibration around electromechanical resonances of the system that can explain the transients observed in the force trace. Different piezo-actuator driving conditions are explored and an account for the different behaviors observed is made. The varying driving conditions do not significantly affect the forces observed, contrary to the theory. It is concluded that the observed effect is a result of coupled vibrations on the torsion balance.