stock/stack

OK, how 'bout this. For me, stock rhymes with walk and stack rhymes with black. However, my experience has been that people from certain parts of the US (which ones?) *more or less* rhyme stock with black. I recall seeing something in a Maximum PC magainze about how to pronounce a word (which I already knew) and they spelled the pronunciation with an a where I would have used an o. I can't remember what word it was. I'll look it up when I get home.