Are all GZ34's born equal?

[Mike Watterson]

I agree with what you say Mike, that doesnt alter the fact that I have found them very noisy.
Perhaps it is a problem of microphony  ?. which again suggests poor construction.

Impossible to hear unless the electrolytic capacitors have either high ESR or very high leakage or almost no capacitance, i.e. dried out or needing reformed.

The waveform with ANY rectifier has massive 50 Hz (half wave) or 100 Hz hum (full wave) with all mains noise (which can be considerable) superimposed if there is only a resistive load. You can simulate effect of high ESR by having a resistor in series only with capacitor. Sounds awful.