Crackle noise from heated, supersonic jets is investigated through high-fidelity large eddy simulation (LES). Simulations of a military-style nozzle reveal that N-shaped waves responsible for crackle noise emerge directly from the supersonic jet turbulence, and thus do not depend solely on nonlinear acoustic propagation effects. Conditional averaging using a backtracking algorithm furthermore reveals intermittent large-scale flow structures embedded in the jet turbulence as a likely source of the N-shaped waves. The skewness of pressure (Ffowcs Williams et al., 1975) and the skewness of the time derivative of pressure (Gee et al., 2007) are evaluated from full-field simulation data, and assessed as metrics of crackle. We test the hypothesis that the crackle level depends solely on the jet velocity (Ffowcs Williams et al., 1975) by comparing three simulations sharing the same geometry, but having different operating conditions so that the velocity and temperature are varied independently.