I have a 56 plate 1.8TDCi Focus, which has had a number of issues this year (replacement fuel filter, injector and turbo intake pipe), but this latest one I have no clue about. From cold, the engine has been making a strange noise when I hit around the 2000 rev mark, it does appear to ease off after driving for a while, but I have no clue what's causing it and it's hard to describe. It's been happening for at least three months and has been to the dealer for the intake pipe to be fitted during that time. They never noticed/mentioned it and neither did I. To be honest I thought I was just being a car hypochondriac after the injector issue.
All being well you should be able check out the engine sound in the attached mp3s. If anyone has any bright ideas, I'd love to hear them. I'm not noticing any issues when driving the car, performance, acceleration etc. all seems as I would expect.