The three terminal regulators do not directly reduce any switching noise created by the imput diodes. Their supporting circuitry (passive components) will likely mitigate or reduce most of this noise, assuming there is any in the first place.
I don't think you need to be concerned, because in a 60hz system, with the typical impedance of the home distribution feed, the waveform speed and current availability just do not lend support to the diode exhibiting switching noise. There is nothing fast about 60 cycles. Standard off the shelf and cheap power diodes like the 4000 series are faster than necessary for this duty.
Whatever is there can be tamed by adding a simple RC snubber across each diode. This will mitigate any snappiness that might exist, but probably doesn't.
It's really a law of diminishing returns. Yes, there possibly is some noise but, it's so minute that if you own an amplifier that is being effected in some way, then I recommend that you return it and get your money back. There is too much out there to choose from that isn't affected by this phenomena because the product is properly engineered.
