We have fabricated an Al based single-electron transistor transistor (SET) whose island is suspended above the substrate. The structure can be considered as a two-in-one device containing a doubly clamped beam and a transducer that converts mechanical vibrations into variations in the SET current. In addition to the regular side gate, a bottom gate with a large capacitance, is placed beneath the SET island for increasing the SET coupling to the mechanical motion. The observed response is reproduced in our simulations, which are based on the orthodox model that considers the fundamental flexural mode of the resonating SET island.