The markets await a closely-watched speech from Federal Reserve Chair Janet Yellen in Jackson Hole, Wyoming on Friday. Investors are looking for clarity on the timing of the Fed's next rate hike, which is expected to come at some point before the end of the year. JPMorgan Chase (JPM) - Get Report chief economist Anthony Chan expects Yellen to maintain a flexible tone on the rate increase timeline in her speech. 'The Federal Reserve does want to raise rates this year,' said Chan. 'Being data dependent they have to keep that flexibility open.' Meanwhile, second quarter gross domestic product was revised lower to 1.1 percent growth, down from a previously reported 1.2 percent. The revision was in-line with analysts' expectations. Consumer spending was raised to 4.4 percent growth from 4.2 percent. Herbalife (HLF) - Get Report shares slipped 4.8 percent after news reports surfaced, saying billionaire investor Carl Icahn may sell his stake in the company. Icahn owns $1 billion worth of shares in Herbalife. TheStreet's Scott Gamm reports from Wall Street.