C751B motors sound rather unique because they are built by Fuji
Electric. In Japan, most proplusion systems are provided by
Mitsubishi Electric or Hitachi.
(http://www.fujielectric.co.jp/company/jihou_archives/pdf/73-01/FEJ-73-01-044-2000.pdf)
C151 motors were supplied by Mitsubishi Electric (GTO-Chopper
ver.). Some 03 series also had Mitsubishi Electric motors fitted,
so they will sound similiar.
C651 motors are probably supplied by Siemens in-house as well.
They are similiar to the Keikyu 2100 series, minus the modulation
(the "do-re-mi-fa-so" that 2100 gives out)
Surely Mitsubishi Electric would want to fit the Crystal Movers
with their in-house motors.