It was called something like 'action02' or 'action2', it was one of the songs that appeared when i checked the box to show mounted music. it was this stealthy/tense electronic song, was maybe around a minute to a minute and a half long. it was kinda basic, like it was some sort of placeholder track.
i last remember it being in the game during august 2023, its not there anymore. i did transfer most of my steam library, including gmod, to a new ssd in october, so maybe thats why it dissapeared.