title: Nuclear test-ban body heard noise near Argentine sub's last position
text: VIENNA (Reuters) - An international nuclear test-ban body that runs a global network of listening posts designed to check for secret atomic blasts detected an  unusual signal  underwater last week near where an Argentine submarine went missing, it said on Thursday.  The Vienna-based Comprehensive nuclear Test-Ban Treaty Organization (CTBTO) runs monitoring stations equipped with devices including hydrophones - underwater microphones that scan the oceans for sound waves. Two of its monitoring stations detected the unusual signal, the CTBTO said in a statement, adding that it was passing the information on to the Argentine authorities coordinating the search for the ARA San Juan, which had 44 crew on board when it went missing last week. An Argentine navy spokesman said earlier on Thursday that an abnormal sound detected near the submarine s last known position in the South Atlantic was  consistent with an explosion , but the CTBTO was more guarded on the possible cause.   It could be consistent with an explosion but there is no certainty about this,  CTBTO hydroacoustic engineer Mario Zampolli told Reuters. He agreed with the navy spokesman s description of the signal as unusual and short, adding that the cause was non-natural.  We can also calculate the time when the event happened in that location and that time is about three and a half hours after the last contact that the sub apparently had, according to what s out in the news,  he said. The stations that detected it are far apart, in the Atlantic and Indian oceans, he added. 