Noise from solid state rectifier in tube amp
Diodes can be noisy when used as rectifiers due to reverse recovery induced spikes. Certain types of diodes perform better (schottky and so-called 'soft-recovery' diodes) or are essentially immune (silicon carbide) to this effect.

A well-designed circuit can address reverse recovery via the use of appropriate diodes (i.e schottkys and/or silicon carbide where appropriate) and by snubber networks, which absorb and dissipate the spike energy.