Hi, sorry if this is out of your jurisdiction but after many hours of google searching I don't know where else to go.
I'm trying to analyse the signals being output from bela using the NI Elvis 2+ as part of a university project however whenever I connect any output of the system to the scope, the test signal is not present and instead the scope shows a wired pulse'ish wave at mains frequency despite the signal being present when monitored directly from bela.
Rather curiously if I connect the 3.5mm output to my headphones, the test signal will be present however if I then touch the input probe of the scope to a contact for either the left or right channel the hum will appear in the corresponding ear.
I've taken some pictures of the board and scope. In the pictures below the bela is supposed to be outputting a 440Hz sinusoid.
I've tested this on multiple elvis boards and the issue is still present, and the 50Hz signal appears when the probe is placed on any conductive point of the bela shield. What am I doing wrong, do I need to isolate?