[sdiy] Signals leaking into the PSU?

[A.M. Barrio]

Hello,
I'm having an issue where the frequency of my VCO is being affected by the
operation of other modules. I'll give a a broader explanation:

I'm a beginner on synth DIY, right now I have my home made case, a PSU, two
VCOs, an LFO, a clock module and an amplifier/speaker (built in the case,
not externally). Everything has been arranged by me, I haven't purchased
any module yet. The clock and the LFO are the latest modules I have built
(pretty much both at the same time), and when I tested them on their own,
they worked just fine. However I noticed that when they are powered, the
frequency of the VCO would stutter following the operation of the clock and
the LFO.

That would be: *without connecting the clock or the LFO anywhere*, just
having them powered up, whenever the clock is up or down, or the waves
generated by the LFO reset, the frequency of the VCO varies a tiny bit. It
gets more noticeable the higher the pitch of the VCO.

After some head scratching I've realised that the signals generated by any
of the modules I have (both VCOs, the clock and the LFO) are somehow
leaking into the +12 and -12 rails of my PSU. Measuring any of the rails on
my scope (on AC mode, so only the noise is shown), I can see that the waves
generated by the modules I mentioned above are there as well in the form of
noise (around 20mVpp each of them). That explains the little variations in
frequency of the VCO. However I have no idea why this is happening or how
to fix it. I have tried with different PSUs I have around:
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