is there a hiss or anything else you could tell us to help you out? Hopefully it's not a valve.
Sounds like a valve, or something else that broke inside of the engine. Whatever it is, I'd get it check out ASAP, or else you will blow your engine if you've got broken parts being thrashed around in there.
Are you sure the sound is coming from the engine, and not anywhere else under the Hood
Also, why the hell were you holding your RPM's that high for so long???