2007 Focus TDCI - Help

[FocusTDCI]

Hi - I own a Ford Focus 2007 TDCI Turbo Diesel. I have been having a very strange problem with the car and was hoping the knowledgeable people on these forums could assist me.

Basically, the car has a "shudder/vibration" when stopped at lights or idling. You can feel it as though it is under the car coming up through it. It is intermittent and not constant.

It is worse when the air conditioning is on. But, it is still there even when air con is off.

The revs stay constant all the time - never drops or increases.

When the air con is on and the shudder is worse it is accompanied by a what sounds like a high pitched grinding/whistle noise when the car is decelerating from about 2000 rpm down to 1100rpm at idle.

I have taken it back to the dealer 3 times and they have told me there is nothing wrong. I have had an independent mechanic take a look at it and he agrees that there is definitely something going on but has no idea what it is or where to start.

Any help/advice would be appreciated. If anyone knows of a really good Ford diesel mechanic east of the bridge in Sydney that would be great as well??