Another heart sound configuration which mimics a split second heart sound is a single second heart sound followed by a tumor plop (a transient which occurs early in diastole).
If you move the stethoscope head to the pulmonic area the tumor plop will disappear. If you continue to hear two distinct sounds at the pulmonic area the likelihood is that you are hearing a split second heart sound.
The timing and frequency of a tumor plop are identical to that of a third heart sound gallop. It is not possible to distinguish one from the other.