help....640D metallic chirping

[NINJA59]

It seems my 65 plate 640D has developed a metallic metal on metal rotational chirping from the front drivers wheel (it is already booked in to be "investigated" on Monday).

But I was looking for wisdom about the source of said annoyance...forewarned is forearmed.

Pointers:
Driving 30-40mph most of the time you here a slight chirping (very obvious when driving past hard surfaces like walls etc.), 70's you tend to hear a bit of a hum (however road noise is higher and it is more difficult to hear).The noise does seem to increase in frequency as speed increases
No juddering or vibration under braking from any speed
In warmer conditions and sometimes after driving 30-40 minutes it becomes noticeably louder with more of a rattle.
It seems fairly constant in some form
I have jacked up both front wheels I found the passenger side had no roughness, the driver side had an additional metallic noise, I could find no play in the vertically or horizontally, bar the extra bit of noise (and possibly roughness).
Turning wise when it has been louder after the 30-40 minute drive it does seem "worse" when turning left than right

Wheel bearing? or Brake Disc/Caliper related?

It has been doing it for 3-4 weeks