Good afternoon.

Plugged into the 1/4 L & R 9/10 inputs on my AR16 is a guitar modeler.  Plugged into the channel 15/16 XLR input is a phantom powered condenser mic.

With all channels muted except 9/10, the green signal light on that channel 9/10 lights as expected when the modeler signal hits it, however...

...so does the one on the 15/16 strip.  Even when the fader is all the way down and the mute switch is depressed.  Any thoughts on why?  I am chasing an unwanted chorusing sound I periodically get on my guitar signal from time to time, and this is currently my mostly likely culprit.