(1) [word] something something [word]
(2) [word] somethin' somethin' [word]
(3) A little something something
(4) A little somethin' somethin'
(5) A little something
Of course it's about something that is not known. My experience is that (1) and (2) are used when someone is trying to figure out a string of words but knows only one for instance, and uses it a bit like a wildcard (something something café you know; i.e. hard rock).
Another use I'm familiar with is when something is (5) (missing) a little something (top ngram); like when someone tastes what you cooked and says that (it's missing a little something, I don't know, salt maybe...).
Is there a difference in meaning between something something and just something when using little (3 vs. 5) i.e. is one less precise than the other? Furthermore, is there a difference in meaning from using the contracted form (somethin' somethin')? Do we generally use one something per missing term in (1) and (2) or is "something something" for two or more? Finally, is there anything inappropriate, or innuendo with using (a) "little something something" (3&4), as in:
Your performance is not on par with what I expected, it's missing a little something something which I would like to see showcased in upcoming events.