This is a "fix" for reverse recovery spikes. Most diodes do not turn off immediately when they become reverse biased, they leak the opposite polarity then turn off. One fix is the diodes that Bottlehead uses, the soft recovery diodes. Another one is using Cree diodes which are costly and hard to find.
A trick someone on the old board told me was to put one Cree diode in series with the positive lead coming from the bridge. It stops the noise.
A choke in the power supply will pretty much eliminate the spikes too.