Dr. Howard Lieberman, a trauma surgeon with the Miami-Dade Fire Rescue task force, told CNN that rescue crews heard 'some tapping' yesterday - or noise indicating that some of the victims may still be alive. Rescue crews 'did hear some tapping - there was some noise,' he said. But he said that the tapping had 'dissipated' by Friday. Still, he said, crews hadn't given up hope. 'We haven't really heard anything in a while now, but that's not to say that there's still not people trapped that are alive,' he told CNN's Sanjay Gupta. 'As time's running out they might be getting a little more sick or ill – not as vocal as before – but, like I said, we're going to keep searching.'