By Caroline Valetkevitch NEW YORK, Oct 11 (Reuters) - U.S. stocks ended a choppy session lower on Monday as investors grew nervous ahead of third-quarter earnings reporting season. Supply chain problems and higher costs for energy and other things have fueled concern about earnings, set to kick off with JPMorgan Chase & Co JPM.N results on Wednesday. While another period of strong U.S. profit growth is forecast for Corporate America, earnings are shaping up to be crucial for investors worried about how supply disruptions and inflation pressures will affect bottom lines.