I have one white and two black ones. None of them 'hum' (referring to the noise that PSU transformers sometimes make). I cannot detect any noticeable difference in sound between three of them. In fact the internals are exactly the same, and according to 'sources' the white ones were built out of spare parts and component leftovers after Oberheim had gone bust and reanimated, so there's nothing special in them. They all are somewhat noisy, but not beyond normal considering the cheap components (TL082 etc.) they were built from.

 

Cheers,
Margus