just to close this off.
Took my car to Nissan Osborne Park today. The noise was happening around the 4k rpm in almost any gear at half throttle.
The mechanic found the turbo intake pipe or some pipe near the turbo was rubbing hard up against the chassis, i'm not sure exact details but they've re-adjusted it.
Auto service (the fluid in there was looking a bit dark)- $330
Throttle body clean (recommended by them) - $135
Diagnose and fix that problem - $70
Replace some cracked belts - ~$120
$700 odd later and hopefully she'll be like new. Will report after I have a drive.
Funny watching one mechanic come and look at the car and he's like 'what's that? Is that an import???'
Altogether they were pretty inquisitive about the car, finding out whether it would hook up to their diagnostics, finding out what belts fit etc.