Is it a whistle almost? Turbos do whine when they spool up they make a distinctive noise. If it extremely loud you could have excessive shaft play. if it is almost a whistling sound your turbo may be near seizing which would restrict air going in the intake side of the turbo and restrict exhaust gases leaving which would make a whistleing noise with the limited amunt of air getting in and out (like when you clasp a leaf and blow on it almost)(does oil leak out at the intake side or exhaust side of the turbo?). It might just be that the turbo was also run to hard and it overheated and fried (no water cooling).
There are a number of things but its hard to tell it might be best to check out the turbo.

 

turbos make a nice whistling sound but it shouldn't be an ear splitter. You might want to take the turbo off and examine it and get it checked out you can have it rebuilt if its necessary. It should only cost a few hundred for a new turbo if that or you could get it rebuilt they aren't to expensive stock.

 

Not long after I got my car I had a loud whislte under boost and the hose from the turbo to the J pipe had a split in it. Then a little later the a similar noise started and I found the turbo to manifold nuts loose making it whistle. As for the emergency relief how do you pull it open, are you sure thats what it is and not the egr. It has a bov(blow off valve) but it is sealed and you cant get a finger on it, unless yu have an aftermarket of some type. The waste gate is attached to the turbo housing and has a vacuum line attached to a servo with a rod coming out of the middle going to the waste gate. You should check it and be sure its opening and closing properly and not binding or froze............

 

The turbos in my car sound like a siren at the right RPM. If the turbo was hammered, it would most likely howl like a banshee if there was excessive shaft play, or it would not make any whistle sound if it was seized. Either way, it's a wild goose chase. Does the car run ok if you slowly rev it up, or does it just run a bit longer before dying? The whistle sound you're hearing, does the pitch or tone change as you increase the RPM's, or does it remain constant? Check all of your grounding points to make sure you have solid grounds. I'm assuming you've changed plugs/wires/cap/rotor. Have you checked the hose between the MAF and the throttle body? Make sure you don't have a crack in that. If you did, then the more the engine moved under torque, the more the crack you open. This could cause your problem. Check all you vacuum lines too.

 

If your Z is sputtering like that, it could be the fuel system or ignition. Is the AFM in good shape? Has the fuel filter been changed? Are all the injectors okay with none leaking? On my ZXT, when the turbo spools, it sounds like when you let air flow past your teeth, almost as if you were trying to whistle through your teeth. Anyways, if you're in the San Diego area, I don't mind trying to help you out.
John 82ZXT

 

Yank off the rubber hose that goes to the turbo and see if the compressor blade has any shaft play. You can check inside the j-pipe after the turbo to see if maybe oil is getting into the intake system. You don't have vacuum leaks do you? Just curious cause it will cause your Z to sputter like crazy. Biggest culprit for me was those small hoses that attached to the vacuum pump for the a/c system. That and the PVC valve hose.
John 82ZXT

 

How did your dad check the output of the turbo? A turbo won't register much output unless you're driving it. Just revving the car up in the driveway won't really do anything. What does you boost gauge read? I think it's a fuel issue. Possibly not enough fuel pressure. Have you tried checking the ECU fault codes?