screeching noise when recording

I’ve been using audacity for a while to record mainly bass and guitar and this is the first time I have this kind of problem… I have no problem recording just one track (everything sounds fine) but as soon as I record a second track I start hearing a screeching noise but when I listen back to what I recorded it sounds fine. WHat can I do?

Turn off “Software Playthrough” (in “Transport menu > Transport Options”).