The mutator is called FlagAnnouncementsV2 and makes use of an external audio package called DefaultAnnouncements.uax.
I noticed that on some CTF servers this audio package has been substituted by another one, called FlagAnnouncementsFix.uax. Anyway this package looks like to be bugged (2 sounds are inverted). When I installed a CTF server for TSF clan, I fixed it and saved it as FlagAnnouncementsFix2.uax.

These are the server packages and the server actor configuration in your System/UT.ini file:

[Engine.GameEngine]
...
ServerPackages=FlagAnnouncementsV2
ServerPackages=FlagAnnouncementsFix2
...
ServerActors=FlagAnnouncementsV2.FlagAnnouncements
...


The mutator FlagAnnouncementsV2 uses an FlagAnnouncements.ini config file, here you have to setup the audio package used:

[FlagAnnouncementsV2.FlagAnnouncements]
bPickupAnnouncement=True
bDroppedAnnouncement=True
bReturnedAnnouncement=True
bDominatingAnnouncement=True
bCaptureAnnouncement=True
bReturnedSound=True
bTakenSound=False
bNewCaptureSound=True
bNoCaptureSound=False
DominationScore=3
VoicePack=FlagAnnouncementsFix2