A bed of sand was fluidized by mixtures of methane and air and the events observed after the gases are ignited were studied. The continuously changing temperature of the bed was measured and fluctuations of pressure under the bed and the noise level above the bed were recorded, using fast response detectors. The results were used to show that bubbles igniting inside the bed gave rise to signals which were of similar character, irrespective of whether they were recorded from above or from below. The records obtained from above and from below were correlated directly, and after modifications, to distinguish between deterministic and random components. This involved frequency filtering and amplitude discrimination. The results obtained showed that in hotter beds bubbles explode lower down. The changes observed in the acoustic signals as the bed temperature rose were compared with the height at which bubbles would be expected to explode on the basis of a simplified kinetic model of a branched chain chemical reaction. The comparison confirmed that there is a direct connection between combustion inside bubbles, pressure pulsations and acoustic effects. It has also been shown that the duration and frequency of the explosions can be estimated using the product of signals registered simultaneously from above and from below.