  In this paper we ask whether the phenomenon of timing noise long known in
electromagnetic pulsar astronomy is likely to be important in gravitational
wave (GW) observations of spinning-down neutron stars. We find that timing
noise is strong enough to be of importance only in the young pulsars, which
must have larger triaxialities than theory predicts for their GW emission to be
detectable. However, assuming that their GW emission is detectable, we list the
pulsars for which timing noise is important, either because it is strong enough
that its neglect by the observer would render the source undetectable, or else
because it is a measurable feature of the GW signal. We also find that timing
noise places a limit on the observation duration of a coherent blind GW search,
and suggest that hierarchical search techniques might be able to cope with this
problem. Demonstration of the presence or absence of timing noise in the GW
channel would give a new probe of neutron star physics.
