I believe that both the Keikyu 2100 and (new) 1000 series EMUs use Siemens VVVF inverters. These inverters have been tuned to emit the "fa-sol-la-si" musical syllables- a bit of whimsy on the part of the electrical engineers. Its always fun to hear these units start up- better that the usual electrical VVVF whine, even though I personally prefer traditional traction motor growl. Interesting side note- Siemens is the only foreign manufacturer to succeed in having their electricals installed in Japanese rolling stock. In addition to the above units, you'll find Siemens equipment on JR East's E501 units (GTO thyristor).