Haver: To talk nonsense, gibberish; to speak rubbish.
One could be told to “stop havering” or “dinnae haver”.
Regional variations may substitute “slaver” in this instance, which also means to drool or salivate, as well as talk nonsense. “Ach, you’re just slavering.”
Perhaps the most famous use of the word “haver” comes from the 1988 Proclaimers’ hit I’m Gonna Be (500 Miles), where the singer confused countless people across the globe as to the meaning of the line. “And if I haver, yeah I know I’m gonna be, I’m gonna be the man who’s havering to you.”
Clearly we’re looking at a situation where the singer is confident that if he ever comes under the influence of alcohol (as per the preceding line of the song) and begins talking rubbish, then the object of his affections will bear the brunt of the garbled conversation.
So now you know.