[Jabouty]

The only real way to diagnose noise issues is to first locate the area of the engine compartment that it's located in.

Start the engine and then stick your ear in the engine compartment and listen to where the sound is coming from. Rev the engine a few times to get a good feel for where it's at, and if push comes to shove you can use a long screwdriver with the handle against your ear as a kind of mechanic's stethoscope and poke around the block abit to see if it's there. Metal on metal squeal as you describe will usually be an accessory, a/c, alternator, power steering pump, etc, or even the turbo as you suggest. But first locate the sound, front or back of engine, driver / passenger, upper lower etc and go from there.