  We solve the Laplace equation $\Box h_{ij}=0$ describing the propagation of
gravitational waves in an expanding background metric with a power law scale
factor in the presence of a point mass in the weak field approximation
(Newtonian McVittie background). We use boundary conditions at large distances
from the mass corresponding to a standing spherical gravitational wave in an
expanding background which is equivalent to a linear combination of an incoming
and an outgoing propagating gravitational wave. We compare the solution with
the corresponding solution in the absence of the point mass and show that the
point mass increases the amplitude of the wave and also decreases its frequency
(as observed by an observer at infinity) in accordance with gravitational time
delay.
