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Discussion Starter · #1 ·
I am a newbie to this forum, having recently purchased a 2006 XC90 2.5T with just shy of 100k for my wife. We bought it knowing that the vehicle had a whistling/squealing noise that happened every time you started it cold but went away when it warmed up. I assumed it to be an old sepentine belt that I could handle myself. Well, on top of finding out that there is no printed repair manual for these cars (an unpleasant surprise), I found that the noise actually seems to be coming from somewhere on the driver side of the engine. It sounds like it is on the firewall side, though it's hard to pinpoint. It is only loud during the higher RPM at startup and during acceleration, and it goes away after running for 5-10 minutes. My wife has tasked me with fixing it...or having it fixed if I don't fix it in a timely manner.

I have read about vacuum leaks and oil trap pans that could be the cause. I've cracked the oil cap and pulled the dipstick to see if it went away, and that doesn't seem to be the source, as there is no pressure buildup in the oil pan. I'm having a hard time tracing the sound, and without a repair manual I feel a bit lost. Some direction as to where to look and what to look for would be greatly appreciated.

One note is that a few times while on trips my cruise control has shut off and won't reset until I turn the vehicle off and back on. Is the cruise run by vacuum? Could this be a hint to where there may be a leak?
 

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We get the same sound and I believe it's the turbo. Not sure if it's a normal thing but so far no problems with the car except for the siren sound. I believe the only true fix would be to change the turbo. Anyone else got a solution?
 

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Had my 2.5T for 3 yrs now, and it's always had a mild whistle on start-up, and under hard acceleration. The engine and turbo are fine--peppy acceleration, and the oil is always clean-looking, even after 5,000 miles. It is a very mild whistle though.
 

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UPDATE: I found my whistling sound. I noticed small drops of oil on my garage this morning. Checked the engine bay found that the turbo hose connecting the intercooler to the pipe running over the engine was not clamped all the way. It was letting a small amount of oil out of the pipe and this is where the whistling sound was coming from. So check out all of your turbo hose to make sure everything is tight. Good luck!
 

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Discussion Starter · #5 ·
xallenx1, thanks for the tip. If you could take a picture of your engine and point to the clamp that was loose, that would be a big help. I'm admittedly not real comfortable under the hood, as this is my first turbo, and I don't have my usual crutch of a repair manual to lean on for guidance.

If anyone has a breakout of the turbo system to show the components and locations, I'd really appreciate it, too.
 

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No picture but you should see a black plastic pipe going over your engine. you can't miss it. Follow it to the fron of the car and you will see a rubber hose connecting the plastic pipe to the intercooler. Check the clamps. Also, check turbo hoses for leaks.
 

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Discussion Starter · #7 ·
I took a look at the turbo tubes (on either end of the hard pipe) and both have a good bit of oil on the outside. The longer one on the front also looks like it may be a replacement that wasn't correct, as the hose seems to flatten at the bends (not a pre-molded hose). One of the Torx screws that mounts the pipe to the engine is also missing (anyone know the thread size for these?), so I think someone had to remove it at some point for some kind of repair. This may well be the source of the noise! It certainly make sense.

I read on another thread where someone replaced these hoses, and they noted a good bit of oil in them. Is this something that I should watch for and be concerned about if I do find oil collected in there? I certainly expect to find this, based on what looks to be seepage from the clamp joints.
 

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Discussion Starter · #8 ·
I finally got around to replacing the two turbo hoses with the silicone set from IPD. That turned out to be a really easy job, and from the look of the old hoses (flimsy and covered in old oil) it was about time. However, the whistling noise is still there. I've not yet found a vacuum hose leaking. During the repair I did note something I hadn't before...that the sound seems to be at least as loud, if not louder, when under the vehicle. I had read somewhere that the catalytic converter can fail and become noisy, though the sound was described more like a "rattle." The whistling noise definitely has a vibrato to it that suggests it's cyclic, like maybe it's the turbo sound amplifying to the outside. Do you think maybe there's leak somewhere in the exhaust system? Other thoughts?
 

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I finally got around to replacing the two turbo hoses with the silicone set from IPD. That turned out to be a really easy job, and from the look of the old hoses (flimsy and covered in old oil) it was about time. However, the whistling noise is still there. I've not yet found a vacuum hose leaking. During the repair I did note something I hadn't before...that the sound seems to be at least as loud, if not louder, when under the vehicle. I had read somewhere that the catalytic converter can fail and become noisy, though the sound was described more like a "rattle." The whistling noise definitely has a vibrato to it that suggests it's cyclic, like maybe it's the turbo sound amplifying to the outside. Do you think maybe there's leak somewhere in the exhaust system? Other thoughts?
you may be hearing the turbo, it does make a whistling sound, especially amplified in things like quiet parking garages
 

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Discussion Starter · #10 ·
you may be hearing the turbo, it does make a whistling sound, especially amplified in things like quiet parking garages
When we bought this car, there were two nearly identical ones on the lot. The other one didn't exhibit this sound at all. My instinct was that it was a simple serpentine belt replacement, but it turned out that I was wrong. The noise essentially goes away after the car warms up, so it leads me to believe something isn't sealed properly. It's just a matter of chasing it down.
 
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