Atem Mini Pro (iso) audio not in sync with Rodecaster Pro

I use the monitor L/R line output of a Rodecaster Pro to feed the Mic 1 of the Atem Mini Pro (two 1/4" TS plugs to 1/8" TRS). But this introduces a high pitched noise that, if I turn up the gain in post, presents problems.
I then try to align the audio that recorded with the Rodecaster, but this does not stay in sync for longer than a few minutes. Any idea on how to either 1) Get rid of the noise during recording or 2) have the audio files sync up better?
Right now they only stay in sync for about 5 to 10 minutes max before I have to make an edit and shift the audio.
I then try to align the audio that recorded with the Rodecaster, but this does not stay in sync for longer than a few minutes. Any idea on how to either 1) Get rid of the noise during recording or 2) have the audio files sync up better?
Right now they only stay in sync for about 5 to 10 minutes max before I have to make an edit and shift the audio.