Roycui There is a book by 'Reader's Digest' called 'Reverse Dictionary' that you might find useful for English language questions and learning. Squeaky clean is a saying that something has really been cleaned well. It probably comes from the noise that newly cleaned shiny surfaces make when rubbed.

Michael is right, also, I think that you could consider this saying "slang". All it means is that whatever you were trying to clean, is VERY clean.