When sending an oscillator (1kHz @ +4db) into a channel and out through the L/R stereo bus or when the oscillator is patched directly into the PRE VCA return, there is a low level but audible ring coming from the stereo bus. When looking at an FFT display it looks like a crazy amount of harmonics bunched together. Oddly adjusting the threshold of the Quad Comp (with the comp not engaged) adjusts the level of various harmonics slightly.
There is also a random pumping (+/- .8db) of the audio. You can see the meters pumping up and down in the video below.
https://youtu.be/Hjs2Snzl-PoWhen I patch into the post fader return the signal is clean (no distortion) and the pumping is gone.
I should also note that the Left and Right channels of the stereo bus are in sync with the pumping up and down. Also, the cards in the center section have all just been recapped.
