Quick Follow up. The HiHy went in last Friday and the ABS actuator was replaced. Thank god it was under warranty because this was 2000 part.

Talked to the tech some more about the issue and they believe that there may be a design flaw in the brake lines that is allowing air into the actuator that then causes the noise. There is supposedly a TSB out on the Prius for this issue. Right now there only solution was to replace the actuator, but there is no guarantee it won't return.

For now the noise is gone, so let's hope it is fixed permanently.