I have a relatively faint high pitched whine if powered by 9v as well. Doesn't matter the source of power; it remains the same with anything I used. I think it's how tonex ones are. 3 so far have all had the same issue.
I think people often don't notice it because of active gating and/or the tone not being high gain enough for the whine to be perceptible. Turning the guitar volume pot down, with gate off, with a high gain capture reveals it.
The moment I power via USB, it goes away.