I have a pine board floor, the fellow who laid it seems to have been keen on a "cottage look" as he laid the boards down with about 1/2" gaps in between and the whole thing is held down with deck screws. (As are the moldings and trim throughout the house, but that's another story...) It's finished with some kind of urethane or varnish that's starting to lift in places and is really worn.
Anyway, aside from the other issues created by this floor - namely the fact that it accumulates debris like nobody's business, and it's seriously prone to damage from shoes, furniture, dropped items and anything wet - I have this one spot in the floor that creaks. I've tightened the screws as far as possible and it helped but the creak is still there. It's inaccessible from underneath, being above a finished rec room in the basement with a tiled ceiling. It's not a joint in the top floorboard; it's square in the middle of a board. Although I suppose it could be a joint underneath in the subfloor.
I've thought about oozing carpenter's glue into the space around this board and seeing if that will stop it from shifting, and I've thought about removing the screws around the squeaky spot and replacing them with longer ones... and I've considered that we may need to take up a couple of boards and look underneath to see what's going on. But I'm open to suggestions!