It's not a distinct cue. It's just cut together from snippets of other cues in the episode.
I'm sorry, but if you hear the cue in other episodes you'll realise it is not a hybrid, stuck-together edited cue, but an original one. A prime example for you to note the detail of the cue is just after the M5 Robot has entered Flint's secret laboratory with the Ryetlayn and McCoy looks at the several bottles of coloured liquid, moving into the scene in which Rayna plays pool, in Requiem for Methuselah. As she prepares to play, you'll hear the cue gradually fade and end.