  Studies of the lensed quasar ${\rm Q}0957+561 {\rm A,B}$ have shown evidence
for microlensing in the brightness history of the quasar images. It had been
suggested that a frequency offset between the brightness fluctuations in each
of the two images might possibly be caused by gravitational radiation generated
by a massive black hole binary at the center of the lensing galaxy. This paper
demonstrates that the fluctuations produced by such a source of gravitational
waves will be too small to account for the observed frequency offsets.
