Sept 25 (Reuters) - U.S. stocks dipped in choppy trading on Wednesday, with the S&P 500 eyeing a fifth day of losses, as a lack of progress in budget negotiations in Washington puzzled investors. The Dow Jones industrial average fell 0.04 percent, to 15,329.13, the S&P 500 lost 0.07 percent, to 1,696.25 and the Nasdaq Composite dropped 0.05 percent, to 3,766.296.