Darkglass Microtubes 900 XLR output sending loud buzzing sound, even when the amp is off.

As stated in the title, the amp sends a crazy hot signal to the mixer, and when unmuted it has a crazy loud buzz, even when the amp is off. We've used it with an old mixer and had no issues, but after upgrading to the Yamaha TF5, the amp doesn't send di signal at all, just crazy loud buzz.