Sprinkle roast on all sides with salt and pepper. Place roast in crock pot; add onion, broth, brown sugar, and vinegar. Cover tightly; cook 5 to 6 hours on high, turning occasionally. Remove roast and set aside. Add crumbled gingersnap to the sauce in the crock pot. Stir until sauce thickens. Slice meat and spoon sauce over slices. Serve over noodles.