Need IDIOM meaning 'to waffle on' ?

In Spanish, more precisely in Argentinian Spanish, "tocar la guitarra/ guitarrear" (or even "mandar fruta") is a colloquial expression to indicate that person is waffling, rambling o beating around the bush because they don't know the answer to a question, especially in an oral exam. Some may argue those three examples in English do not entirely convey the same meaning as the Spanish phrase as they lack the ingredient of conning or lying while in the process; it's not just using lots of word to mean nothing.

Anyway, I happened to hear a short while ago someone provide an idiom, probably endng with the word 'letters' that may be the closest in meaning to the Spanish saying. Any idea what that may be?