Screeching noise on boost - please help!
 

Hi everyone,

I'm at an impasse with my 2006 Spec D WRX STi 2.5. Since I've had it, it has created a loud scream when on boost, (no it's not the passenger, I gagged them to make sure).
Research initially pointed to an up-pipe gasket, but the noise only happens on boost and the pitch and volume does not change with engine revs so I don't think it's that. Performance seems unaffected and ECU is telling me boost pressure is around 18psi give or take.

Things I've changed:

• Inlet pipe - new Samco
• All vacuum lines - new
• New BOV
• New inlet manifold gaskets and bolts
• New TGV valve spacer gaskets and bolts
• Had the complete inlet assembly off, checked and re-assembled
• TMIC pressure tested fine

Recently, when driving "spiritedly" the noise begins further and further up the rev range until eventually disappears - heat related is my guess, but then returns once cooled off a bit.

Can anyone shed any light or offer any advice on what to check next please?

Have you taken the TMIC off yet and checked all of the silicone pipes under that to the turbo and inlet for cracks or holes? That would be my first point of call. Sounds like a silicone boost pipe leak to me.

Have a look at the blades on turbo also to make sure there is no damage to them as that'll cause them to squeal...first hand experience of that :(

^^^^^^
The turbo outlet to intercooler elbow have been know to get chewed up by the OEM (perforated type) jubilee clip and leak.

This is also a very good call once you've checked all the silicone pipes.

The thinking now is that it's not on the cold side, it's the up-pipe gasket leaking from back pressure when the turbo is at full spool. Great, PITA job...

I had something that sounds similar to what you're describing... With mine it was the gasket between the turbo and downpipe, basically one of the 5 studs/nuts was missing/chewed up... it looked like the nuts had been reused at some point. To cure it was a new downpipe gasket, studs and nuts. Unfortunately still a pita job...

Hope it helps,

Chris.