Distorted backing track underneath voice recording

Hi all
I produce radio shows in my studio and have been using Audacity for 5 years now, generally without issue. I use this with Virtual DJ - running the tracks from there, and recording voice over start and finish of tracks, recorded as a “live” show. Lately I have found when a song, or show intro is playing and being recorded, and I switch the mics on to record audio over it, it distorts the song, or show intro. Sounds garbled, if that makes sense. Never used to happen, and it obviously effects the production quality. I know it’s not Virtual DJ and all other performance levels are fine with Audacity. It’s just when the two are combined the problem happens. Any thoughts? Using the latest version of both. Thanks.

Apparently Virtual DJ does not do AutoDucking , only manual …