I think I'm having the same problem here... Interestingly mine happened straight after my 37.5k service on my ST3. I'm convinced Ford did this.

It's been back into Ford several times and they can't work out what or where the noise is (muppets) and have finally said you'll have to live with it and see if it gets worse!!! Could be the turbo they said, costing £2k. Jeez.

What a joke....

Anyway, I searched on-line and saw this post and I'm convinced this is what I've got, cold start, whistling noise raising with revs. Mine's bluefin'd and it makes the noise around 2000rpm.

Gonna do the test with the dipstick and then get straight onto Ford and get it in.

I hope Ford do this FOC as they have clearly damaged the unit.