Stock markets today ended the week on a slightly sour note, with the barometer Sensex snapping 4-day rally and slipping 26 points. After trading in a narrow range through the day, the Bombay Stock Exchange benchmark Sensex settled at 19,966 point, shedding 25.77 points or 0.13 per cent from the previous close. Similarly, the National Stock Exchange's wide-based Nifty declined by 18.90 points to close at 5,992.Analysts said, investors turned cautious on market regulator SEBI barring four companies from trading and booked profits, ignoring positive economic data from the US.