Synth into Octatrack Thru machine inputs has weird blip artifacts for note off

Elektron Gear Octatrack
#1

I have tested this by bypassing the Octatrack and then using its input with a Thru machine on a track.

When connected straight into my mixer, there is no problem.

But with my synth going into Octatrack inputs C D with a Thru machine, there is a blip noise after the release phase of the note (on numerous presets). The same noise is also heard when changing presets, so not only for audio! – some strange signals OT is hearing.

Example here:

Why would it do this?

I’ve turned the global gate on the Octatrack inputs to -inf (effectively off).
There are no FX on the track or on the master.
Audio CC is set to off.

Yet this strangeness presists…

#2

That noise appears before even the release stage of the amp EG is completed (this is seen in the second, long release sound) like if there was a threshold being crossed triggering that noise. That points to some sort of gate or amp envelope modulation on the OT’s side. Usual question: did you check with a blank project?

#3

That might be just the audio sync, because I had to do join the audio and video separately.

Good idea, when I next get a chance I’ll check on a blank project!