  We present observations of high-amplitude rapid (2 s) variability toward two
bright, compact extragalactic radio sources out of several hundred of the
brightest radio sources in one of the 30x30 deg MWA Epoch of Reionization
fields using the Murchison Widefield Array (MWA) at 155 MHz. After rejecting
intrinsic, instrumental, and ionospheric origins we consider the most likely
explanation for this variability to be interplanetary scintillation (IPS),
likely the result of a large coronal mass ejection propagating from the Sun.
This is confirmed by roughly contemporaneous observations with the Ooty Radio
Telescope. We see evidence for structure on spatial scales ranging from <1000
km to >1e6 km. The serendipitous night-time nature of these detections
illustrates the new regime that the MWA has opened for IPS studies with
sensitive night-time, wide-field, low-frequency observations. This regime
complements traditional dedicated strategies for observing IPS and can be
utilized in real-time to facilitate dedicated follow-up observations. At the
same time, it allows large-scale surveys for compact (arcsec) structures in
low-frequency radio sources despite the 2 arcmin resolution of the array.
