  Alfv\'enic fluctuations of various scales are ubiquitous in the corona; their
non-linear interactions and eventual turbulent cascade result in an important
heating mechanism that accelerates the solar wind. These fluctuations may be
processed by large-scale, transient, and coherent heliospheric structures such
as coronal mass ejections (CMEs). In this study we investigate the interactions
between Alfv\'enic solar wind fluctuations and CMEs using magnetohydrodynamic
(MHD) simulations. We study the transmission of upstream solar wind
fluctuations into the CME leading to the formation of CME sheath fluctuations.
Additionally, we investigate the influence of the fluctuation frequencies on
the extent of the CME sheath. We used an ideal MHD model with an adiabatic
equation of state. An Alfv\'en pump wave is injected into the quiet solar wind
by perturbing the transverse magnetic field and velocity components, and a CME
is injected by inserting a flux-rope modelled as a magnetic island into the
quasi-steady solar wind. The upstream Alfv\'en waves experience a decrease in
wavelength and change in the wave vector direction due to the non-radial
topology of the CME shock front. The CME sheath inhibits the transmission of
long-wavelength fluctuations due to the presence of non-radial flows in this
region. The frequency of the solar wind fluctuations also affects the
steepening of MHD fast waves causing the CME shock propagation speed to vary
with the solar wind fluctuation frequencies.
