What can cause CV16 Out#16 to be "High"?

[mgd]

Hi Forum,

I'm experiencing a droning sound after I hit SHIFT+STOP twice. The culprit is CV16 Out#16 stilll being "high".
I'm out of ideas where to look for possibly causes.

What can create that behaviour?

I've configured all odd numbered outs -5 - +5V and use them for notes and all even numbered outs 0 - +10V used for gates. All gates are "low" except out#16.

Any hints welcome,
Michael