'Static/Distortion' when certain Tracks Selected

I’ve noticed since Cubase 8 - and on into 8.5 - that selecting a specific track (it appears to be completely random which one) causes the audio of the entire project to be come distorted, like static.

I’m currently working on a small project with 12 tracks. When I select the ‘Violas’ track the entire project playback is distorted.

The VI involved doesn’t seem to make a difference.

Also, when I select the Tempo Track and Group Tracks the same problem occurs.

I’ve searched the issues threads and can’t find a mention of this, so wondered if anyone has a suggestion as to what it could be?