CHICAGO (WLS) -- Chicago police are investigating a sexual assault a few blocks from the Lollapalooza festival Friday night, police said.The sexual assault happened at about 11:45 p.m. on North Franklin Street in the Loop, police said.Police said a 28-year-old woman was walking on the sidewalk when two males forced her partly inside a dark-colored SUV and sexually assaulted her.The victim refused medical treatment, police said. Further details on the crime were not immediately available.Area Central detectives are investigating. No suspects are in custody, police said.