I went to best buy a little while ago and I played the demo of Steel Diver and I noticed when I hit the sea floor it rumbled. I wasn't impressed with the slow nature and awkward controls of Steel Diver, but the rumble was a big surprise. I don't think it was built in rumble but via the speakers. The music is very minimal in the game and it seemed to use BASS to make a rumble on the top of the 3DS unit whenever you hit a sea wall. I went home and tried some songs on the music ap with strong bass and indeed it works . The top screen slightly rumbles because of the speakers which is normal to any speaker system and high bass however to my knowing this is the only game to use this to emulate rumble. Could other programmers use high bass to emulate rumble in games? Nintendo obviously did in Steel Diver.