High-pitched noise in audio on iMac Pro 2017

Are you using a usb audio interface?

It seems, this discussion should continue here? Did you try a different audio interface in the meantime? I have absolutely no issues with my iMac Pro and a Thunderbolt Quantum 2 by Presonus.

Weird :) Clicking comes in different flavors, usually makes one think of mechanical drive failing or clocking mismatch, but that typewriter thing? Hmmmm? And after careful repeated listening and consulting with experts...that definitely is a squeal :) I would say boot as another user to see if the OS X sound prefs got hosed. Barring that, go into the user library (make it visible by holding option while going to Go menu) and remove any Apple sound or audio preferences, and move the whole plugins folder to the desktop so it boots without any plugins. Maybe something in the Reaper routing is causing it to feedback? If you don't have a alternate user to boot as, create one in the Users And Groups System Prefs from the left menu, and allow it to be an admin. This will create a new Reaper setup from default as well as for Apple, and also of the interface software, if it has any.

What drumphil said. Its the Dragonfly IMO. Which COLOR of dragonfly do yo have as that sample rate must match the sample rate in the AMS setup in OSX on the Mac