  Decayless kink oscillations are ubiquitously observed in active region
coronal loops with an almost constant amplitude for several cycles. Decayless
kink oscillations of coronal loops triggered by coronal rain have been
analysed, but the impact of coronal rain formation in an already oscillating
loop is unclear. As kink oscillations can help diagnose the local plasma
conditions, it is important to understand how these are affected by coronal
rain phenomena. In this study, we present the analysis of an event of coronal
rain that occurred on 25 April 2014 and was simultaneously observed by
\textit{Slit-Jaw Imager} (SJI) onboard \textit{Interface Region Imaging
Spectrograph} (IRIS) and \textit{Atmospheric Imaging Assembly} (AIA) onboard
\textit{Solar Dynamic Observatory} (SDO). The oscillation properties of the
coronal loop in AIA are investigated before and after the appearance of coronal
rain in SJI. We find signatures of decayless oscillations before and after
coronal rain at similar positions to those during coronal rain. The individual
cases show a greater amplitude and period during coronal rain. The mean period
is increased by 1.3 times during coronal rain, while the average amplitude is
increased by 2 times during rain, in agreement with the expected density
increase from coronal rain. The existence of the oscillations in the same loop
at the time of no coronal rain indicates the presence of a footpoint driver.
The properties of the observed oscillations during coronal rain can result from
the combined contribution of coronal rain and a footpoint driver. The
oscillation amplitude associated with coronal rain is approximated to be 0.14
Mm. The properties of decayless oscillations are considerably affected by
coronal rain, and without prior knowledge of coronal rain in the loop, a
significant discrepancy can arise from coronal seismology with respect to the
true values.
