Strange gargling sound coming and going

We have a very good system in our theatre that has worked well for years but just last week we ran into an issue, when we powered up the system for a concert we were running that evening (this is a high school), there was this gargling sound, almost ocean like sound coming from our house speakers. Fantastic, we used a backup system that we pulled out of storage and that was that but now we're trying to figure out the cause.

The problematic sound seems to come and go, we checked everything. The only thing that I noticed that was different/slightly odd was that one of our two equalizer's screen was blinking. That little LCD status screen was just sitting there, blinking its backlight on and off at a constant rate. At one point later while trying to figure out the issue I noticed it was no longer blinking, none of our equipment was giving an errors or anything. Just that single equalizer screen blinking. I am not in the theatre right now so I can only tell you that the two equalizers are DBX DriverRack PA's.