A causal relation is shown to exist between the cycle-to-cycle variability of the pressure-time trace and the noise radiated from a single cylinder, direct injection Diesel engine. Measurements conducted over a range of load and speed include spectral analysis of the p-t trace and the radiated noise as well as coherence measurements between the cylinder pressure and noise signals. In the spectral analysis of the p-t trace, a signal averaging technique is used to separate the periodic part of the trace from the random fluctuations superimposed on the periodic part. In the data reduction scheme account is taken of the effect of imperfect speed and load control on the results. The results are supported by knowledge of the randomness of turbulent combustion in other flow systems.