Sounds like it might have been a bull snake--in size and coloration they resemble a rattler, but in behavior, more like a black snake--beneficial.
Had them in spades when I lived in Oklahoma. You'd find them in the barn, and they'd vibrate their tail in dry hay or whatever. Even knowing there were no rattlers in our area, you'd instinctively jump at that sound. Bull snakes loved to hole up in the stone-built storm cellar underneath our house (which is why my wife went down there only reluctantly). I went down one time, and ducking below the doorway (short framed door) I looked up to find one coiled on either side of the door frame inches above eye level. I kept a spring-loaded clamp arrangement on the end of a broomstick to grab them and carry outdoors.
My favorite snake story, as told to me by my Okie neighbor, Gator. Gator once worked as a plumber's assistant, and was in the crawl space under a house, pushing his tray of tools before him on the way to some piping. Just as he came through a gap in a stem wall he said "the biggest bull snake you've ever seen" came past a few inches in front of his nose--carrying a live rat in its mouth. Gator said he came out of there backwards, the fastest he'd ever moved, scraped hell out of his head on floor joists. He said he'd never been in a crawl space since, and would not go in the future.