High pitch whistle at start up, even without belt on

[Pickle']

hi guys,

I have a 2006 ve v6 omega, the last few weeks i've been getting a high pitch noise that i thought was belt/pulley related. So i've changed the belt. Didn't fix it, so i thought i'd start the car with the belt off and its still there. It sounds exactly like a belt/pulley and only lasts 2 or 3 seconds and only as i start the car. Doesn't matter hot/cold its always the same. Any clues as to what this is before i take it to the mechanic would be appreciated.

Thanks in advance.

 

[Sabbath']

Check for a vac leak, or somewhere pulling in air that it shouldnt.

 

[Pickle']

will do, thanks mate.

 

[Capsule]

Does it go away if you pull the oil dipstick out?