Terminating an audio line-in signal when source is disconnected
I wonder if that's really a balun or just a straight-through connection?
Anyway, the output impedance of &quot;line out&quot; is apparently in the 100-600 ohm range. So if you want to try a passive solution I would start with a 1k resistor across each line. This will attenuate the output somewhat along with attenuating the noise. If it's too much, add 1k resistors in series with each other; if it's not enough, add one in parallel.