High volume (pink) noise on outputs of Vi 64X32 MADI stagebox with Vi7000 when using talkback

I have a problem where the oscillator on the Vi7000 console is seemingly sending pink noise to the outputs of the Vi 64X32 MADI stagebox despite the oscillator not being on, or routed to the outputs of the Vi stagebox, at well above the nominal (approaching +22 dBu) level. It seems to be triggered by either raising the talkback level control from off, on the console, with microphone routed to console talkback inputs, or microphone plugged into local rack mic inputs 1-3 and sending to auxes routed to stagebox outputs. It seems to engage suddenly and in pairs. I'm wondering if this is possibly a firmware issue as I've not had this issue previously and the only big change is removing a connection to a second Si console via Madi. It's prevented us from being able to use any of the Stagebox outputs/returns, being relegated to the local rack only. Additionally - the noise doesn't meter on the console at all - the only way of detecting it is from the outputs of the stagebox connected to our monitor processors.