Huge noise floor on Carl Martin Delayla XL when powered, also in bypass

[rockhorst]

Someone asked me to redo the power cord on a Carl Martin Delayla XL. The cable was torn up where it meets the enclosure, so I cut of a piece and redid the wiring. The effect is mains powered, running on 230V and converted down internally with a transformer. I didn't try the pedal before doing this, so don't know if the following problem was already there or something new, but...the noise floor is enormous! The noise level is about halve of the guitar level, basically unplayable. This is both in bypass as when the effect is on. But, when I remove power from the pedal it's completely clean in bypass mode (and no sound when the effect is switched on of course). So in bypass, without power, you have a normal guitar signal, but with the power cord plugged in it makes a lot of noise, I think probably white noise. It does this with the board in and out of the enclosure. I did notice the transformer is very close to the switch itself. Any clues?

This isn't an actual picture of the unit, but looks otherwise identical.