EJ205 boost squeal noise
 

I've got a blobeye WRX with the EJ205 engine which is pretty much standard.
It has started making this noise (attached mp3 file) when under boost. As you can hear it comes on quite abruptly when applying power. Only occurs when the engine is under load, so can't recreate the sound on my driveway.
The recording was done with mics placed on top of the suspension turrets, so the location of the sound appears to be coming from the turbo area as you would expect.
I've just taken the turbo off as I've been chasing an oil leak, and it made the sound before I removed the turbo, but seems worse now. The turbo turbine seemed to be fine (vanes look ok, no excess play) when I gave it a once over.

I've now fitted a temporary boost gauge to try and see if there's anything odd going in with the boost that's related to the noise. Here's a short recording of a 2nd gear bit of acceleration and the noise kicking in around 0.5 bar of boost. Not the greatest capture of the sound unfortunately. When should the wastegate start to open on a standard EJ205 setup?

Couldnt get the clip to work

You need to inspect all boost hoses for loose or broken clamps, most importantly tears or holes in the pipes also.

Could be manifold or up pipe gaskets also. Although not sure if they squeal when leaking, the up pipe has to be tightened in a specific order to get a good a good seal, learnt from experience :norty:

if standard intake pipe they sometimes tear right at the clamp by the turbo. Although usually that causes rough running also

The host to the solenoid had a bit of crack where it joined the connector, but I cut off the offending bit, so that should be OK. I also replaced the gaskets between turbo & up-pipe, and turbo & downpipe, and made sure to torque those up correctly as I also suspect they were leaking. I'll have another look at the intake pipe, though I hope it's not that as it's only few months old.

I replaced the wastegate actuator as it's a relatively quick thing to try, and that made no difference to the noise.

Here's another video to try and get some clues. This time I've videoed the turbo and wastegate actuator as I accelerate. You'll hear to squealing noise come in a couple of times.

Very hard to help with this one without being present. Now you say you've replaced up pipe gaskets etc. You've checked all your hoses. Now on lift off in your video the actuator seems to open when you lift off which is a little suspicious. By rights after changing the actuator you should at least have the map checked cause of different spring rates. Now onto the last bit if you can get a borescope and have a look at your compressor wheel I suspect it mightn't be in the best of shape. Is it by any chance a vf turbo.

This new wastegate actuator didn't seem to make any difference to this noise happening compared to the old one. So I don't think the actuator is the problem now. It's a standard TD04L turbo and the last time I looked inside it, it wasn't in bad condition and didn't have excessive play, but I'll have another look.

The TD turbos are generally strong enough but the vf turbos don't like being over spooled/boosted the fins tend to break off. Just another thought your pcv isn't stuck is it?

The PCV valve itself is pretty new, replaced it a few months ago. However the breather hoses are really flaky and have just ordered a new set, so I'm hoping replacing those might help.

If it's not air escaping somewhere, then maybe a washer or something similar vibrating - perhaps the retaining circlip on the wastegate arm. Small dab of copper-grease might then fix it.

I've now replaced the PCV breather hoses, and the PCV valve itself appeared to be fine. I also retorqued the downpipe to the turbo with fresh nuts. But still get the noise. I don't think it would be the circlip as something that small couldn't generate that level of noise (it is louder than the engine when you're driving).

I had something very similar to this, turned out to be boost air escaping the rubber between the intercooler and throttle body.

Finally found time to do a bit of a strip-down and put everything back together to see if anything looked bad. I removed the downpipe, up-pipe, intercooler, turbo to look over them. Nothing looked particularly bad, or at least jumped out as obviously causing the noise. The only real thing of concern was the gasket between the turbo and downpipe which has a bit of carbon skid-mark on one of the corners, so that's my prime candidate. Those nuts on that junction are a bit of a bugger to get good access to, so torquing them up properly is tricky.

Anyway, I put it all back together and took it out for a short drive, Now it's even worse! The noise kicks in a lot earlier with very moderate loads. So something has got worse on the reinstallation process. So I'm now thinking it's possibly this gasket, as nothing has been replaced and the only things that can really change by taking things apart and putting back together is gaskets getting pressed and things torqued up differently.

I've finally cleared the noise it seems. I decided to go a bit belt and braces:
- Rebuilt the turbo with new bushes, seals, etc. (I already had a turbo rebuild kit).
- Fitted the original stock up-pipe, so not using the de-catted aftermarket one. The original one is a lot harder to fit (more of the case the turbo oil drain pipe is harder to get to) than the de-catted one. Lots of swearing!
- Fitted new gaskets for the downpipe and up-pipe to the turbo. Used aftermarket ones here this time.
So amongst all this work something seemed to solve the problem. Not really sure which thing fixed it, but I'm happy it doesn't sound like crap now.
I don't think I'll try messing around to work out what caused it for now, so I'm a little frustrated not to know the cause.