2008 Vauxhall Vectra Squealing noise

If the noise is only present when youre driving then I doubt its a belt. It sound like a clutch slipping. Does the car seem sluggish, and do you notice any kind of burning smell?

It's only really when I move off and sometimes when I'm in 5th, 6th gear going up hill, only lasts around 3-4 seconds then disappears, no definitely not sluggish and no burning smell, my dad reckons there may be a bearing loose in the alternator?

Oh ok then. Look at the flat side of the serpentine belt, if its very shiny then that will cause a squeal like yours. Your dad is right about bearing squeal but typically they'll make some noise all the time. Open your hood at idle and give a good close listen to the pulleys. If theres little chirps or the like, take a spray bottle with plain water and mist the belt to see if the noise changes. If it does that eliminates the bearing. If it doesn't change or if theres no noise to start with then take the belt off and manually spin them one by one. Check fr difficult to spin and up/down, in/out play. If that's all good drive a little with the belt off to see if it still does it. Then its internal in the engine or the driveline

Thats brilliant, thanks for the advice.

Youre very welcome