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The flow-excited acoustic resonance in shallow rectangular cavities can be a source of severe noise and/or excessive vibration. This phenomenon is excited when one of the acoustic modes in the accommodating enclosure is coupled with the flow instabilities resulting from the shear layer formation at the cavity mouth. In this study the effect of placing a high frequency vortex generator (control cylinder) in vicinity of the upstream edge of the cavity on the acoustic resonance excitation is experimentally and numerically investigated. The effectiveness of the passive method is studied by investigating different cylinder diameters and locations on both horizontal and vertical directions. The study included two cavities with different aspect ratios (L/D=1.0 and L/D=1.67, L: cavity length, D: cavity depth) to address the effectiveness of the method with respect to the cavity depth. The method is investigated in flow with Mach number up to 0.45 and found to be effective in suppressing the acoustic resonance excitation. All the different configurations investigated are compared to the base case which is the bare cavity with no cylinder attached. It is observed that using the optimum cylinder location and diameter can be very effective and able to keep the acoustic pressure below 140 Pa, compared to the base case with values exceeding 2000 Pa. To further understand the interaction between the cylinder vortex shedding and the shear layer at the cavity mouth and the influence on the shear layer thickness, a 2D numerical simulation using a detached eddy simulation models has been carried out and compared to the experimental results.