iTunes Distortion

There is noticeable distortion when my mastered MP3 are played through iTunes. There is no distortion when it is played outside of iTunes and on other systems. I am mastering to -12db more or less. The only time there is no distortion in iTunes is when I master to -23 LUFS. There is no transient peak above 0db. Why is there distortion? I

I also noticed that reference material and other tracks in my iTunes library do not have distortion. One track in particular has no distortion but is metering at -10 db with transients of 1.3 db yet it plays mostly fine. It is a great mystery to me. Perhaps there is a simple answer?

Is it possible to post a sound file to this forum? I tried to do so but w64 and mp3 files are not allowed. I would like to see if this issue is occurring on just my PC only.

This turned out to be an iTunes driver issue. Lots of problems with iTunes out there. The fix was to re-install iTunes from Appleā€™s website.