>> what we're picking up is a great lead. >> reporter: officials say the sounds detected were not of natural origin and likely from a manmade device. but scouring the sediment at the bottom of the ocean will prove difficult. >> the silt on the bottom will complicate that search. >> reporter: today's search efforts intensifying as resources comb the shrinking search area, roughly the size of south carolina. so far, the debris found has not been linked to flight 370. adding to the urgency, the dying batteries powering the black box pinger now past its 30-day expire rags date. >> the signals we picked up recently have been much weaker than the original six signals we picked up. so that means probably we're either a long way away from it or, in my view, more likely, the batteries are starting to fade.