Turbo 95, high pitched noise coming from back of head
 

So I just finished pulling my motor and replacing my oil pump in my 95, it has a rebuilt stock 95 motor with around 180k on it. The car was driving fine yesterday until all of a sudden I noticed a high pitched sound. It almost sounded like an intercooler pipe popped off from inside the car. When I pulled into my drive way the noise persisted. It sounds like its coming from the top left hand side of the engine, it is a loud scream. Car has a brand new throw out bearing and pilot bearing with less than 1k on both items.
What I know about the noise:
-comes from upper left hand side of engine bay
-not a belt, alternator, or ps pump (no ac)
-is not affected by clutch in or out
-EDIT: It does go away under engine load and varies in sound when under vacuum, goes away when in boost, so it seems to be a vacuum leak
-also sounds like it goes away when the engine tachs down
I drove the car too school today which is basically 10 minutes away, sound didn't change at all. I know tracking down noises can be tough, so thanks for your time. I checked in M.net and couldn't find anything. I'll see if I can upload a video of the noise soon.

What made you to replace the oil pump?

Relief valve got stuck, car would not build oil pressure

Fuck if I know what that noise is, but damn is it annoying.

Sorry if this is something obvious, but have you tried a mechanic's stethoscope with a friend working the pedals? I'm terrible at locating sounds, but a basic one (Lisle 52500 off Amazon) makes everything way easier.

you should be able to get it down to an exact location yourself, especailly since it is constant. would be much tougher if it only did it when moving.. We cant track it down from across the interwebz.

So far I've re-seated my injectors (I though there might be a vacuum leak there), replace fuel rail, fuel filter, egr valve, fuel pressure regulator, and the thing that bolts to the front of the intake manifold (I forget the name of it of the top of my head). I get the whole track it down thing but it's SOOO god damn loud I cannot find exactly where it's coming from. I did however have some success in making it go away after I pulled my fuel pressure regulator on and put it back on but it then started to happen again after a 5 minute drive. Still open to ideas, I know noises suck to track down but I'm just looking for ideas.

Why don't you try removing the vac line that goes to the fuel pressure regulator and see if that does anything to the sound.

Still nada, I found a similar sound from a video where the OP said his throttle body was bad. Is it possible for this to happen even without the IACV hooked up?

You can use a long screwdriver as a stethoscope, stick pointy end to things that can make noise, then your ear to the handle. It's not as nice as the Lisle tool but can point you in the right direction.

well, air is still being drawn through the IAC, even with power disconnected, but less so as the engine warms up, so I would expect the noise to change as the engine warms. Even if you use a hose from your ear to
various engine parts, you can't trace it down further?

from what I can hear the sound gets increasingly louder as I move from the throttle body back towards the rear of the engine. I replaced my CAS, just because I had a spare one lying around. The sound starts a few seconds after start up and when I shut the car off it dies of with the sound of the engine, so it's definitely vacuum related. I pulled my throttle body off to try and clean it. I didn't remove the bottom part because the screw's wouldn't budge, made no difference, even though I was pretty sure that's not it anyway.

if you reseated your EGR valve, did you use a new gasket?

This sounds similar to a subaru's screaming banshee uppipe gasket if the flange is warped. Just higher pitched if it's a smaller flange.

have any carb cleaner? theres a trick where you spray carb cleaner around and listen for a change in the sound of the engine. That could help lock in the spot.

I've tried the carb cleaner and had no luck, egr valve seems to not leak as well. My next replacement will be the throttle body

Is there anything one can spray that has a UV dye that can be aerosalized but won't hurt the engine? Locating the leak will be so much more helpful than starting to replace things without knowing what's what.

If you have a gasket with layers (like the ones for the exhaust manifold) those loosening up a bit can possibly cause a whistling sound if air is passing through an area there. Are those all on tight? Anything in the path of air, other than the IC piping if you're not having a boost leak.

this my reason to suspect a bad TB, same exact noise that I have. Also when I removed my TB to try and clean it, when I sprayed carb cleaner into the IACV it all leaked out, which shows it has a bad seal if I'm not mistaken, which is what the guy in this video said went wrong with his upon further inspection. That's my logic for replacing my TB