An easy way to test all the ancillaries at the same time is to remove the auxiliary belt and start the engine. If the noise goes away you can be certain the issue is with the tensioners or a bearing in either the alternator, ac compressor or power steering pump.
It's then a case of identifying the component.
To remove the belt is a fairly easy job.
1. slacken the front right wheel nuts, lift the car ( try not to use the car's jack as they are made from cheese ), place an axle stand in a suitable location and remove the roadwheel.
2. Remove the plastic access hatch by unscrewing the two screws and popping out the plastic rivet.
3. With pencil and paper, draw the path the belt takes around the pulleys.
4. Through the access hole, put a deep offset 15mm spanner ( like this http://www.ebay.co.uk/itm/Silverline...UAAOxyThVTbil2
) on the movable tensioner ( looks like this http://www.ebay.co.uk/itm/ALFA-ROMEO...AAAOSwnGJWSyT4
) - the nut in the centre of the black wheel in that picture - and turn the spanner anticlockwise against the spring as far as you can ( about 90° ). While you hold it there get someone to ease the belt off the ac compressor pulley or the idler pulley. Watch fingers!
5. Remove the belt from the car.
Start the car to see if the noise goes away. If so, and with the engine off, rotate the various parts by hand to see if you can feel a rough bearing. You can also wiggle the pulleys to feel if there's any slop.
Rethread the belt, slacken the tensioner and get your assistant to ease the belt onto the last pulley. Again, watch fingers!
It can be done by one person but I'd recommend two doing it if it's for the first time.