The autocorrelation function of vibrational frequency fluctuations of the CO ligand in carbonmonoxy myoglobin, C-delta delta(t), is computed from molecular dynamics simulations. Electrostatic interactions are assumed to dominate the modulation of the CO vibrational frequency. The simulated C-delta delta(t) is consistent with linear and nonlinear infrared spectroscopic measurements. The short-time decay of Cda is dominated by dynamics of the distal histidine, and of a water molecule that can occupy the heme pocket. Correlated protein and solvent dynamics induce spectral diffusion of the CO frequency on longer time scales.