Strange humming noise while idling

[Dave_Obsession]

First things first, yes it's not the engine...... :togo:

I swear it's only been the last couple of days......start it up.....and while it's idling.....there is the slightest low whirring noise...very quiet...it sounds a bit like an amplifier running, except i only have the factory one at the moment, and it does this with the radio off.

sounds like its coming from somewhere at the back end of the car.

doesn't appear to affect driveability or performance, but now i've heard it, it bugs the hell out of me.....dunno if it's just me hearing things, but I'm positive it wasn't there a few days ago.

Does anybody have any idea what it could possibly be???

Dave