I have the Monomachine rigged up with two pedals and a little mixer.
With the pedals switched on there is a background hum which stops completely if I touch any of the pieces of gear (including the monomachine), suggesting it is a grounding issue.
Do you have the power for the two pedals daisy chained? Then a dedicated pedal power supply with isolated outputs MIGHT help. But I doubt it. Try using two separate PSUs for both pedals and see if it makes any difference.
What will definitely help is a stereo DI box with ground lift, or alternatively two of these boxes: