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5TS is the 'boring' Onyx IIRC. After all, I've been nurtured to appreciate the exquisite delights of a Class 365
Networker Express from a tender young age, and if you dare call that boring... Let's just say it won't end well
Depends on your point of view, the modulation and control method on the Onyx system is much more intresting than the single source exciter and GTO systems on the 323, Networker and 96TS, although the noise on the latter is much more intresting.
The thing is, Power Electronics moved on very quickly, after PWM control came in, the actual semiconductors moved on to include GTO and working with a static convertor, and then what we have now with full wave inversion on three phases, made possible by the joys of MOSFETs coming into common usage to be able to form up IGBT sets...
This article may help;
http://www.railway-technical.com/tract-02.shtml#GTO
I think the noise comes about due to the current to the motor being quickly turned on and off at differing rates, i.e pulse width modulation.
This brings to mind a recording I made, if anyone enjoys the sound:
It is due to the motor controllers but the only motor control out there that uses PWM to actually DRIVE the motor (before anyone harps on about CTBCs and control systems using "PWM" as my trainer said it, that isn't actually PWM). The only LUL stock to use PWM in it's raw form is the 1992TS on the Central Line. An example from Network Rail tracks includes stock such as the Class 321 units, or any of the later DC motored stock.
GTO Systems only use PWM as part of the exciter and do not form an integral part of the system's control, as this can be done without any actual control to form the excitation source for the AC signal.
Modern systems do use PWM (in a very clever way that I won't go into today) to make 'fake' AC for the motors, without going into how AC motors work vs. DC motors that I don't think would be appreciated, I can't really explain much more than that.