Hello, I have a question about an old Digitech GSP-21, if anyone knows that machine.

Here's my concern - when I sustain a note, be it clean or dirty, it cuts very suddenly rather than fading out. There's a "bump" and then it drops out. It sounds as though there's a noise gate, but I turned everything neutral on the unit and it's still there.

When I bypass the machine, the note lasts much longer, is far more dynamic, and fades out naturally. Thoughts?