  We consider the Einstein-Hilbert action without cosmological constant in
5-dimensions and implement the Kaluza-Klein (KK) reduction by compactifying the
fifth direction on a circle of small but finite radius. For non-zero
compactification radius, the 4- dimensional spectrum contains massless and
massive KK modes. For the massive KK modes, we retain four KK tensor and one KK
scalar modes after a gauge fixing. We treat those massive KK modes as
stochastic sources of gravitational wave (GW) with characteristic dependences
of the frequencies on the size of the extra dimension. Using the observational
bounds on the size of the extra dimension and on the characteristic strain, we
make an order estimation on the frequencies and amplitudes of the massive KK
modes that can contribute to the GW.
