Whining VF23 normally means a broken fin on the compressor wheel - especially if it has ever been run up past 1.45 bar (21.03 PSI). I've lost a few this way. Back in Switzerland my mechanic fitted KKK compressor wheels as a replacement successfully but as mentioned above these turbos are not serviceable except by a specialist. VF24 or 28 for a cheap replacement, vf34/35 or TD05 for a bit more power....with the TD05 being the best choice because it is a tough bugger, will never break and if you keep it long enough to wear it out then service kits are still available.
If you want to check it is the wheel, you'll need to remove the inlet hose a little and get a dentists mirror in there. Using a torch you should then see any fin damage.
Dave - which 2.5 though; EJ25 or EJ257. My '97 Legacy EJ25 runs nice
so if its a broken fin is it still safe and will last without causeing any damage?? were would fin have gone then??? presumeing straight into engine???
No, fin will be in your intercooler somewhere. As long as it is not too loud it will be fine - risk is that the wheel is now unbalanced; these things spin pretty fast (150-180,000 rpm ), so it could end up self destructing.
Also worth noting - if it is a broken fin, and you are still hitting target boost, the air charge will be hotter than it was before (turbo is less efficient with a fin broken) which could lead to problems with det if it gets bad enough. Do you have a knocklink to monitor for det? This is unlikely....but possible!