I have recently changed to 2.0L Titanium Auto to protect my worn out left knee. Recently on my 06 2.2 Titanium X Tdci I noticed what I can only describe as a `whistle sound' when changing gear, 1st to 2nd and 2nd to 3rd, it was quite obvious and louder if I changed on a fairly high rev. The sound came with the `over run' between gears and I assumed it was an idler or bearing in the gearbox preparing to fail. I am not mechanically minded but in my car which I had had from new, and was at 58,000 miles, I knew every squeak and rumble intimately. Although I have to say I have had many Mondeos and loved every one of them, so squeaks and rumbles were few and far between.

I arranged to have my local Dagenham Motors look into it after they expressed puzzlement over the phone. Before I could get it to them the rear box of my silencer fell off, jammed and I had to get the RAC to remove it. During the interim I still had the whistle when driving and eventually took the car into the garage to replace the box and listen to the `whistle'.

The box was replaced and when the car was returned they told me they could not detect a `whistle' and sure enough neither could I. It seems that when my rear box was preparing to fall off I developed a warning `whistle' when changing gears? I don't know what caused it but if you should hear an unusual `whistling' sound when changing gears get the rear exhaust box checked before it falls off, like mine did, at 40 mph.

We could have included your car in the "Focus car band" that's being formed from cars exhibiting strange sounds, so far we have, clicks, sighs and now whistles, any more to add? :D

lol, sounds to me like it was corroded, if I am not mistaken, the car has a DPF?

I suspect that the pressure between the turbo and the rear box with DPF was high, and there was a fracture in the pipe, probably the high pressure between these parts caused the excess pressurised air to escape through the crack causing it to whistle.

Glad to see its not whistling now!