Whilst the meaning/intention of the voice messages may be "mysterious", the general purpose of the signal is not - it's for ionosphere research:<p><a href="http://elpub.wdcb.ru/journals/rjes/v10/2007ES000227/2.shtml" rel="nofollow">http://elpub.wdcb.ru/journals/rjes/v10/2007ES000227/2.shtml</a><p>Scroll down to "Doppler Radio Sounding of the Ionosphere", note the broadcast frequency.<p>My guess is that the occasional voices are either a) someone else randomly broadcasting on the same frequency, b) some technical hitch at the broadcast station. Whatever the reason, 99.9999% it's going to be totally mundane.