Base Left: Paradoxical Split of the Second Sound (S2)
A paradoxical split of the second sound occurs when there is a reversal of the normal closure sequence with pulmonic closure occuring before aortic. During inspiration the second sound is single, and during expiration the second sound splits.
The paradoxical splitting of the second sound may be heard when aortic closure is delayed as in marked volume or pressure loads on the left ventricle (i.e. aortic stenosis), or with conduction defects which delay left ventricular depolarization (i.e. left bundle branch block).
The sound you heard is a paradoxical split second sound.