Hello all,
I've had my 2005 WRX STi for a couple of months now and a couple of weeks ago I took it to ScoobyClinic for a winter service, general once over and a power run just to fill in any blanks from the cars history which I may not have been aware of.

I drove away happy, the car was healthy once a couple of niggles were sorted (radiator top hose was fouling the alternator belt and the car had a dodgy ball joint) and I even uncovered a Whiteline anti-lift kit had been fitted to my car previously.

The car made 315bhp on their rollers, the graphs apparently looking healthy though they meant nothing to me!

Big disclaimer here: I AM NOT SAYING THAT SCOOBYCLINIC BROKE MY CAR! I haven't done many miles in my car since owning it, and I've not spent a lot of my time boosting it around everywhere so there's every chance this whistle has been present prior to my SC visit - it just happens that I went away for Christmas on a 120mile round trip so noticed the noise more often when being a bit more spirited through the Yorkshire Dales.

I spent quite a bit of time on the drive home trying to reliably replicate this noise, and it's not 100% of the time but when it does kick in - the following conditions must be true:

Car is in at least 4th gear.
Noise starts when the boost starts (roughly 3k RPM) but then stops at roughly 4k RPM, it's not present all the way through the range.

The car is a standard-ish PPP car with a K&N panel filter and the previous owner had it remapped (hence the 315bhp I guess). The car still appears to have the factory recirc valve fitted (rare, I know).

I've been trying to figure out whether the car feels down on power, but that's difficult because I've not had the car long - and the fact I'm getting used to the torque and acceleration means the rush I got in the first few days has died down... if that makes sense.

I've done loads of searches on the forum and whistling noises on boost seem to range from blown up turbo's to split pipes to incorrectly seated airbox lids - but more often than not it seems to indicate some kind of boost leak. Perhaps a blowing exhaust too(?)

In order to narrow down my search I'd like to know what components SC would be likely to have removed/reseated/etc as part of my service and dyno run so I can check them first.

If the Dyno graphs really are healthy in terms of Boost and power - that suggests to me that perhaps any problem may have been present since the car finished the Dyno run... if that makes sense.

I've recorded a couple of video clips to try and capture the sound:

(Listen for particularly: 9 seconds, 20 seconds, 42 seconds)


This video is putting my foot down in 4th then changing up to 5th so you hear the whistle twice:



Dyno Graphs:

BHP/Torque


Boost/Fuel


I'm hoping somebody can help me at least narrow this down, there's every chance it's just part of the Scooby soundtrack which I've yet to get used to - but I'd like to at least check it out first before ignoring it/living with it.

I've had the bonnet open and engine running and can't see/hear anything unusual - but then again I'm really not sure what I'm looking for :|

I'd like to stress again that I was very impressed with the ScoobyClinic and they were a great set of guys, I don't believe they've "broken my car" but it's too far a journey for me to pop back and have them give it another once over unless I can be sure there's a problem!

Much appreciated for any pointers.

 

Could be as simple as a belt slipping slightly as it comes on boost, quite hard to hear though. I would check the alternator and air con belt are tight and in good condition, if they seem ok you could remove them and go for a quick blast to rule them out, just don't go to far though as your battery wont be getting charged without the alt belt on.
Always best to start with the simple things.

 

Oh, it's funny you should say that.

When I say SC sorted a few niggles out - they changed both my AC and Alternator belts as one of them had been rubbing on the radiator top hose (which they also replaced) so it sounds like we could be onto a winner?

I'll go have a fondle now... but to be honest I've got no idea what's too tight or too loose on these! Can they be tightened by adjusting the wheels, or does it suggest an incorrect belt has been fitted?

Many thanks!

 

They are both adjustable via sliding adjusters, simply a matter of slackening the pinch bolt and adjusting the tensioning bolt.
Correct tension on a new belt should be 7-9mm on it's longest side. It may just be one of them has bedded in after renewal.

 

Thanks alot, much appreciated. I stuck my head under and they all "feel" tight when I fondle them, but it was too dark to see properly so I'll try again tomorrow.

You've put my mind at rest a bit, I guess a slipping belt would explain the intermittent nature of the sound as a leak would be consistent I guess.

 

Me again...

I've had the plastic cover off today to have a proper look at the belts. The belts look both new and nice and tight. There was marginally more play in the AC belt though so I tightened that ever so slightly - but it was still within the 7-9mm flex before I made the adjustment.

I went out for a drive and unfortunately the whistle is still present, but whilst doing all my driving with the music switched off, I actually uncovered another noise which only happens when I've got the AC switched on. I eventually traced it to happen each time the clutch thingy kicks in on the AC unit under the bonnet, so perhaps the two sounds are related/linked?!

I took another video of the under-the-bonnet experience, but it's also audible inside the car. It's very hard to appreciate the sound on the video, but I'm wondering if it could indicate something else.



Is it possible my AC belt is actually too tight? Causing strain on the AC pulley and hence the noise I hear when the AC is switched on?

The 3k RPM noise is consistent regardless of whether or not the AC is switched on.

I'm half tempted to get a local garage to just re-fit both belts and see if that cures it. I'm not sure I'm confident enough to do it myself!

 

Hmmm interesting! I would be tempted to remove the a/c belt temporarily, it's a quick easy check to see if the 2 noises are related. Remove a/c belt but refit the alternator belt and go for a drive (not as if you need the a/c at the moment).
It's not uncommom after having a new belt fitted for a bearing to fail in say alternator or a/c pump. It's quite often the case that it has been on it's way out, but with the old belt being on a while it's not tensioned up quite as much, when a new belt is fitted and tensioned up properly it puts it under more stress and basically finishes it off.
At a guess i would say the a/c pump has some resistance making it harder to spin hence the belt is struggling to turn it, and just beginning to slip when under heavy load/torque conditions i.e coming on boost.
Just a theory, but removing it will prove it (or not).

 

If a belt is too tight you will usually hear a consistent humm from it.

 

I've just watched that again and it maybe just the angle the video is taken from, but the tensioner pulley for the a/c really doesn't look like it's moving! Like it's seized!
Check that is free before anything else.

 

boost leak, check vac hoses and all hoses around intake, IC and manifold, check them thoroughly for splits and that they are tight.

could also be exhaust leak, upipe gaskets etc should be checked if not the above.

 

Hmmm I didnt pay much attention to the bottom pulley tbh (im guessing thats the tensioner!) I'll check it tomorrow as im out now.

I may be brave and take the belt off completely on sunday which will either nail the ac unit or rule it out, in which case I guess its time to hunt for leaks as per Barnshaws post! Fun fun fun.

 

Yip as above... I had a whine screeching noise when on boost and after looking the data we thought up pipe gaskets, but I then changed all clamps to Mikalor and it it fixed my my prob, good luck...

 

I dont suppose somebody can make me an annotated diagram of the relevant tubes/hoses to check? Im trying to learn but it seems that my engine bay changes everytime I look at it

Very helpful so far though, many thanks

 

Just a thought, would a boost leak record an ODBII message? Ive got a reader but it came up clean.

 

Me... again

I've just been out now (again) in the dark with a bottle of soapy water and a torch

First off, the tension pulley for the AC is spinning fine.

The hoses all look fine, no signs of leaks, holes, etc. I did however notice a puff of smoke/gas/steam/something or other come from underneath the turbo.

I leaned in with the torch and had a look - and I could see a little bit of moisture on what (I guess) is part of the exhaust system/headers? I've circled the spot below.



I revved the engine and a little bubble appeared in the moisture! I legged it round to get my camera and when I got back the water had evaporated.

I filled a spray bottle up with soapy water, and went back out and covered that area with soapy water then gave the engine a few revs - sure enough the bubbles started in the moisture and got bigger the more revs I gave it. On idle, no bubbles at all came out.

Do you think I've found the cause of this noise? If so - what's my best course of action? Can a generic exhaust place/garage temporarily patch this up just to see if it cures the issue? I can't tell if the part I'm looking at is a join (hence potentially a gasket change) or whether it's just a ridge in the metalwork which has broken, hence replacement part I guess.

 

I've worked this out to be the downpipe, which according to my certificate should be a PPP downpipe with sports cat.

If this is indeed broken, am I going to struggle to get a replacement Prodrive unit and hope to land lucky with a forum/ebay seller?

 

Looks like your cat downpipe is split or cracked. If so can generally be welded to repair if its a good ppp sports cat. Will need new gaskets and bolts for back up. Get a good garage to have a look to be sure.

 

Cheers Phil, I'm trying to get hold of a local guy with a good reputation - my detailer recommended him and his garage.

Hopefully he can tell me whether the damage is terminal or not. At the very least I'd like someone to try bodging a band-aid fix so I can prove whether this is the root of the whistling, then I don't mind splashing cash on it!

 

No worries Fonzey. Not sure if that would work as pressure will be quite high and difficult to hold the gases back. As you said get the downpipe off asap.
Cheers Phil

 

My local mechanic isn't convinced that the sound is caused by a leaky down pipe...said he'd expect it to be more raspy. I told him about the bubbles and he said that could be explained by heat alone.

I'm still pretty sure the pipe is leaking though. I showed a friend my wee trick with the soapy water and he's confident too. The bubbles are pinprick bubbles from a specific point, and occur even when the car has been started from cold and revved just once.

I'm tempted to finger a bit of that gun gum paste over the weld on the downpipe, let it cure and then go out for a quick blast.

I know the paste won't hold a leak on the downpipe due to the heat and pressures involved, but if I get just 10mins without whistling then I can happily get the pipe off the car to be repaired or replaced knowing its not a wild goose chase.

If the paste holds though and the whistle persists...then its probably time to divert attention elsewhere.