Slow magneto-acoustic waves are frequently observed in sunspots. The running penumbral waves in the chromospheric penumbrae of sunspots, are believed to be due to upward propagating slow waves. Umbral flashes occur due to the formation of shocks by upward propagating waves. Propagating coronal disturbances along fan-like loop structures, are also thought to be due to slow magneto-acoustic waves. With the recent observations, it is becoming increasingly evident that all these phenomena are connected, but the source of the oscillations is not clearly known. Although the photospheric p-modes are often assumed as a possible source, there is no compelling evidence so far. Here we present our recent study on the observed modulations in amplitude of the slow waves to address this issue. We employed multi-wavelength data to identify the exact source by tracking the waves as they propagate through different layers of the solar atmosphere.