It's normal to have a small amount of induction noise I.e. Quite owl noise. But if you have just noticed it it's probablies the turbo deteriating ... Are you running any kind of non standard map?
When mine went I had a loud wining noise on spool up and down (kept thinking police were behind me, that's how loud it will get) that was about a week before it went accompanied by 1 or 2 clouds of blue smoke and then bang it went ... When thinking of changing it just be aware that when the turbos go in these they typically go out in style, breaking the shaft and shredding the compressor wheel, feeding oil straight into engine so if your not quick enough to stop the engine; worst case can lead to bent rods... This isn't gospel but just from my experience.
I would recommend turbotechnics for a recon turbo as they come with 2 year warranty (same as new part from dealer) think mine set me back about 560 with posting my old one to them.. They also do a hybrid option from which I gather are good for around 200bhp (I think) other than that you can go down the route of companies that cut and re-weld cast manifold on larger turbo option to fit bkd (company on ebay sells them) or buying a tubular manifold and fitting gtb2260 or larger (300bhp with accompanied mods). All gets a bit expensive if your looking bigger than a standard/hybrid turbo... Hope this helps ��