I've run into an unexpected problem.
It seems that when I use both scope channels within the same circuit (at least for this circuit) I get tons of 60Hz noise and its harmonics. Using a single channel does not generate this kind of noise.
I am using a 3 channel DC supply plugged into 60hz wall power that feeds my breadboard circuit in two areas. My breadboard circuit is a simple non-inverting op-amp whose input signal comes from a constant current source excited thermistor. The gain is ~ 30 V/V. I'm using the Analog Discovery 2.
Normally, I've been using the either channel to check my pre or post-amplified signal. This single channel behaves normally. Nice low frequency temperature response from my thermistor.
However, upon adding the other channel to look at the opposite end of my op-amp circuit, I get tons of 60Hz, 120Hz, etc. garbage.