  The Alfv\'en wave (AW) is the most common fluctuation present within the
emitted solar wind from the Sun. Moreover, the interaction between
interplanetary coronal mass ejection (ICME) and high-speed stream (HSS) has
been observed on several occasions. However, can such interaction generate an
AW? What will be the nature of AW in such a scenario remains an open question.
To answer it, we have investigated an ICME-HSS interaction event observed on
21st October 1999 at 1 AU by Wind spacecraft. We have used the Wal\'en test to
identify AW and estimated Elsasser variables to find the characteristics of the
AWs. We explicitly find that ICME were dominant with Sunward AWs, whereas the
trailing HSS has strong anti-Sunward AW. We suggest that the ICME-HSS
interaction deforms the MC of the ICME, resulting in the AWs inside the MC. In
addition, the existence of reconnection within the ICME early stage can also be
the leading cause of the origin of AW within it.
