G'day. New guy here. Long time motorcyclist, recent WRX convert. Bought an MY94 six months ago, all original except the plumbed BOV. Only 110,000 kms on this fantastic little car. Runs and drives like new; well it did until recently!

Gave it a bootful a week ago and took it up to redline in 1st gear. Has made a whizzing noise under boost since, the cause of which I'm yet to locate. Seems to be coming from under the bonnet rather than through the exhaust, heard equally from both front seats. Turbo area I guess.

I've sought opinions and advice on another WRX forum but they don't seem too enthusiastic or mechanically interested. I'm sure their cars have nice looking wheels though.

I've been over the inlet tract from MAF to throttle body and all hoses, clamps and pipes seem ok. Save a leak in the intercooler, the inlet manifold or the turbo itself I guess I can rule out a boost leak. Hooked up a (crappy) boost/vac gauge to the manifold which shows boost steadily increasing to 10 or 11 psi at 5500 rpm. Can't remember the vacuum reading at idle. Engine idles and responds crisply.

Suggestion has been made of a leaking exhaust manifold to up-pipe or up-pipe to turbo gasket. Pulled off the heat shields from around the manifold/up-pipe join and from around the turbo but can't see or hear signs of leaks. Also had a shop do a quick test by sending smoke back through the exhaust but again no obvious signs of gasket leaks (though the CAT is probably toast). But given gaskets are cheap I'm considering changing them anyway, to rule them out if nothing else.

Questions:
1. Is it possible to change those 2 gaskets by separating the up-pipe from the manifold and the base of the turbo, without removing the turbo's oil and coolant lines and with only separating the down-pipe from the turbo*(not from the rear of the exhaust)?

2. Any other ideas of what might make a whizzing noise under boost?

3. How might I determine whether or not it's the turbo itself?Is it just a matter of eliminating everything else first, then pulling the turbo off for inspection?

Thanks in advance.
Ballbag.