Wow, this is a bummer.
I use the Pyramid CV/Gate and ENV every day with my eurorack modular and have never experienced anything like that. I’m so sorry, what a hassle.
It sounds to me like bona fide ground looping.
Is the power supply going into a surge protected outlet?
Is it on the same outlet as the modular?
Is the modular grounded?
Do you have another CV/Gate device you can try the pyramid outs on? Does it happen there too?
Do you have another sequencer or VC source (like an SQ-1 or something else) to make sure it’s not the modular case?
I would try to get the modular and the pyramid onto the same circuit, and be sure that everything connected is grounded, and there is no larger appliance in the chain - fluorescent lights, a computer, etc.
Try to connect the pyramid to a power strip, and the modular to the same strip, and then be sure that strip is plugged into a clean circuit with nothing else connected.
Strip everything back to a bare minimum to have as few possible sources as possible to eliminate potential problems until you can see if it’s the power, the modular’s power/case/ground or the pyramid.
If it’s not the power, and it’s not the case, then something’s gone wrong in the pyramid and it needed to be repaired or replaced.
What a bummer. I’m so sorry.