I confess i’ve never heard the expression. To me it suggests an infant, suckling ineffectually at its mother’s bosom --- most infants suck some wind, which must subsequently be expelled as a burp (oh most musical of words!), or belch, or grepps (Yiddish), or borborygm. In a figurative sense, the exprssion suggests working hard at some activity, with little tangible benefit. Of course all this is purest speculation, but as languagehat recently reminded us, what isn’t?
I wouldn’t trust Internet usage about anything to do with language. One of the most horrifying things about most users of the Internet is their ingnorance, and consequent shoddy misuse, of the language they are trying to communicate in. This site, language-wise, is like a tiny island of light in an immense ocean of darkness --- that is one of the reasons why I love it.