weird hum in 888/24

[aurix1]

I don't know what's wrong. But since a week ago my 888/24 has been making this weird hum. The thing is, only in output 2, not any other! When turned on, there's no hum, but, as soon as it warms up for a while... voilá. Sometimes it gets loud, and you can hear it decrease (or increase) its volume, sometimes it even disappears.
I figured that it could be something about my electric installation. But I don´t know... I've never had that problem before! and how come it's only in output 2?
I've already trashed digisetup (just in case), and doesn't gets any better..?
I can still work and rout my mix to any other output... but, that noise is worrying me.
What to do?

thanks, guys!

(off the record, I will move some gear around and look for a missing groud or an electric loop...)

[DigiTechSupt]

-Reseat the interface cable at both ends as well as the audio cable connected to output #2.

-If the hum persists, the interface is most likely the problem. Contact tech support for an RA at: 650-842-6699

Brent