This paper presents an experimental investigation of the vorticity shedding and the susceptibility of acoustic resonance excitation for a square tube array with an intermediate tube spacing (i.e., pitch-to-diameter ratio (P/D) of 1.73). The tube array could be rotated about an axis normal to the flow direction so that the effect of the flow approach angle could be investigated. Various Strouhal periodicities (St) were detected, and their strength and value were dependent on the position measured within the tube bundle and the tube bundle's angular orientation. However, not all of the Strouhal periodicities measured caused self-excitation of acoustic resonance. This work illustrates the importance of considering the flow approach angle in the heat exchanger design phase to avoid the undesirable effects of acoustic resonance excitation during operation.