|sounds like a collection of junk (dust, spilled soda, boogers, fingernail clippings, etc) got into your keyboard and is causing pressure in one place to cause contact nearby.|
you can try taking the keyboard apart to clean it, but you stand a decent chance of breaking it in the process. since keyboards are like, 5 dollars, i would just try a different one on your current machine. if the problem persists, you've got a really weird issue on your hands. if a new keyboard fixes it, your old keyboard is junked and just be grateful they're not more expensive to replace and no data is stored on them.