Preface: I don't know if anyone will be able to diagnose what's wrong with my unit from this description, I'm mainly posting as a curiosity. I've already contacted support, and they recommend I send it in, which I'll probably do.
When I power on my QC, there's a loud buzzing on the input. Not a 60hz hum, but a 20-30hz clicking. It happens with or without anything plugged in, whether the input is set to mic or instrument, ground lifted or no, phantom power or no, at home or any other grid I plug into. I've never used anything but the factory-supplied power adapter. While it's happening, the input meter reads close to 0db. After 3-4 minutes the buzzing abruptly stops.
If I power it off then
