My Line 6 TonePort UX2 has suddenly started malfunctioning. It is absolutely fine for playback, but on all the inputs (Mic 1 & 2, + instrument) there is terrible digital white noise maxing out the input levels, even if I disconnect all input devices. If you plug in a guitar cable and touch the end of it you can hear that it is picking up something from the input, but and musical signal is completely drowned out by noise.
I've unplugged and replugged the device, and I've rebooted Windows (I'm using Win 7). I'm running the latest drivers and have even reinstalled them. Changing the buffer sizes in the control panel doesn't help either. Does this mean something is actually broken in the hardware? Or are there any other software troubleshooting steps I can go through?
Update I've made another discovery. The noise on the inputs only appears when I have one or the other of my monitors (Alesis M1 520s) plugged in to the UX2's outputs. If I disconnect them and work with headphones then all is fine. The thing is, they don't even have to be powered on for the noise to appear.
Update 2 I can also fix the noise by not using the HDMI output on my laptop (which is connected to an LG monitor). I'm guessing this means I have some kind of nasty ground loop going on?