Beats me, sorry. Bot Spotters are trying to solve another "Who are those guys?" mystery (Part 1 [webmasterworld.com]; Part 2 [webmasterworld.com]), but this sounds completely new/different. Hmm. A few Qs, please?
-- Are the hits to .html files only? Or do they get graphics with .html? What about other file types like .txt, .mov, .ico, etc.?
-- Regardless of file type, are your 'multiples' visitors hitting the same files? Do they came back again, and do it again?
-- Are the User-agents different, from host to host, and/or from visit to visit?
-- Are the hits rapid-fire, akin to a robot, or is the rate more 'human'?
TIA for helping ease my curiosity, even if I can't ease yours!