My oscilloscope channel 2 is showing a signal (2.5V P/P, 88MHz, roughly sine wave) when :
channel 1 ground, channel 2 ground, and channel 2 probe are all connected to the same point in my test circuit
channel 1 probe is connected to a different point in my test circuit.
Channel 1 is showing the same shape with 4.5V P/P.
I don't understand why my channel 2 is showing a signal when its probe and ground are connected to the same point. What could I be doing wrong?