I would suggest you see if the squeek dissappears when moving the steering wheel of dabbing the brakes. Annoying squeaks can come from front brake pads, although you say not, because of dry shims or dust build u p in the calliper. By dabbing the brakes you lessen the gap between thepad and disk and the squeek will go also by moving the steering the angle change of the front wheels can have the same effect.

The cure, if this is the case, is to remove dust with an air line and if this doesn' stop it then remove the pads and put a minute smear of copper slip, and I mean minute, on the back of the pads.

Whilst wheel bearings is an alternative they usually are constant and sound quite harsh whilst the brake theory is just an annoying little squeak, rather like Ronnie Corbet perhaps. I don't think that sitting stationery would cause it whilst the above possibility would worsten or come on as the brakes cooled and tolerances increased allowing the squeek to reappear.

I have an Audi A6 with the same problem which goes when the brakes are hot but reappears when cold. Initially when you start in the morning the disk has a light corrosion on it due to overnight dampness. This is quicky removed with the pads but adds to the dust and the problem. Once the disk and pads are warm then the noise gradually goes untill they cool off when it can annoyingly reappears. I have dusted them out withan air line, the bearings are fine and as it is just from the offside I have ignored it as I am sure it is in need of what I suggest earlier with the copper slip grease, time will eventually let me resolve the problem.

OLDMINIMAN