I have recently run into this exact problem.

I did not have any problems when I was testing the pedal with the included power adapter after I had just received it. The noise came about after I started using the Freeze with my other pedals, all hooked up to the same power supply.

However! The high pitched sound disappeared in rehearsal today when I threw in the Freeze before a Line6 M9. By then I had by coincidence taken out every pedal except the Freeze from the power supply, the M9 running on a separate power adapter. Either the M9 magically fixed it somehow, or using the Freeze on a power supply together with other pedals is the problem.

I want to use the Freeze at a gig next week, so I shall investigate further. I will report back with my findings.