I know it's coming up on 10 years since the last comment on this post but the description of the noise is spot on to what I'm experience. Came across this when looking for belt tensioning tips.
"The noise almost sounds like getting a key cut, except the noise is amplified and higher pitched"
Just thought I'd take a long shot and ask if you were able to fix this? It started happening for me right after I replaced all three accessory belts which cured my cold start belt squeal. Been playing with tension on the belts, no luck. This noise was not there prior to replacing all three belts.