Actually the Trek image I knew most from the show before watching it was from the silly early-Internet proto-Meme, Leonard Nimoy Should Eat More Salsa.

I don’t even remember seeing this before I googled it just now.

I could be wrong because this isn’t something I know much about, but I think what they did to make the Tribble sound was probably pretty normal for what it took to create unique sound effects back then. If you didn’t do that then you were just stuck with whatever existing animal noise you wanted to use.