Getting a lot of noise with FX8 MK I

[In Absentia]

I’m using the 4CM without using Humbuster cables. My amp is very high quality with a great loop (Carol-Ann Triptik 2). It sounds a bit like 60 cycle hum. Once I disengage the loop on my amp, it goes away, so it is definitely isolated to the loop. Running the pedalboard Pre, I have the cleanest sound in the world. Only when I change to the loop do I get the noise. Any ideas?