On a rotating, aspherical earth, coupling between spheroidal and toroidal seismic free oscillations is manifested in the tine domain as a slow alternation of the oscillation envelope between the transverse and the radial and/or vertical motion components. Using a narrow-band smooth envelope estimator, we have observed this behavior in data from the MS=8.1 Macquarie Ridge earthquake of 5/23/89. Rotational coupling is the principal cause of mixed-type coupling for f<4.2 mHz. However, envelope perturbations consistent with mixed-type coupling are observed for 0S38--0T36 and 0S37--0T35, which do not couple through rotation, and couple only weakly through smooth upper mantle velocity models. Such envelope perturbations can bias estimates of modal Q, and suggest that scattering may play a role in the attenuation of long-period surface waves. ¿ American Geophysical Union 1990