Confined acoustic vibrations of GaN nanorods have been observed using ultrafast pump-probe spectroscopy. Depending on the fabrication method, the geometrical properties of the nanorods are different and the detection of a given vibration mode can be favored. In bottom-up fabrication, the extensional modes are detected. The detection mechanism of these confined acoustic modes is briefly presented. Breathing modes are more easily detected in top-down fabrication. From the observation of the breathing modes, the diameter dependent elastic properties are extracted. The influence of the surrounding on the confined vibration is also studied.