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Discussion Starter · #1 ·
So I’ve been having this issue ever since I got my 4bt swap running over 6 months ago. I have yet to find the cause. It’s basically a howling or air leak sounding noise that seems to get worse with boost, and goes away almost completely when I let off the throttle. It also only seems to do it once the engine gets up to around 160 degrees or so, so it never makes the sound when I first start driving.

It’s super annoying because from inside the cab it sounds like it’s coming from everywhere. Also I can hear the normal turbo whistle, and this sounds nothing like it. I thought at first it was a small boost leak since I seem to have no problem building 20 pounds of boost. I pulled the intake off and pressurized the compressor side of the turbo and did hear a tiny bit of air leaking out from behind the compressor housing around where the snap ring holds the compressor housing on, but this was just a small hissing sound and not a loud howl. I put some red rtv around that area as a temporary fix, as air was leaking out with hardly any pressure at all. I could barely even feel it with my hand. The best solution might be to take the compressor housing off and clean the surfaces and then put the snap ring back in. In any case I could not re-create the noise whatsoever by pressurizing the intake even with the engine warm.

I’m wondering if it could be exhaust related or maybe even something internal to the turbo itself (hopefully not), though the turbo does not appear to have any shaft play. Turbo is an HX30W. I took the video below of my boost gauge while driving. I tried to floor it and then let off the throttle a couple of times. The noise sort of comes in and out at times and is not always consistent even when boost is steady.

The only other thing I can think of, and it may be a long shot, is if the vacuum pump and/or brake booster is making the noise but only while the engine is loaded.

Here's the video:

https://www.youtube.com/watch?v=Z-biCgGd-PU&feature=youtu.be
 

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Discussion Starter · #2 ·
I tried pressurizing the intake up to 20psi and cannot replicate the noise. I can’t hear any air escaping anywhere along the intake side, but the pressure bleeds down relatively quickly once I turn the air compressor off. I took some pictures of the compressor wheel. It doesn’t seem to have any real shaft play when pushing or pulling on the shaft, but I can shift it up and down and side to side a little, though not enough for the wheel to touch the housing. The intake area looks clean where the blades are very close to the housing due to tight clearance, but it doesn’t look like the housing has been in contact with the compressor wheel. Maybe the only strange thing I see is that one of the blades has a sort of white stain on it you can see in the pictures. I’m not turbo savvy enough to tell if I have a good turbo or if it’s on it’s way out.

I cannot replicate the howling noise at idle or revving at idle. It has to be making boost and the engine has to be around 160 degrees or higher. It’s loudest on the interstate when I’m making over 10psi.
 

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Do you have a boost gauge, if so what is the boost pressure?
Any exhaust smoke when it is making the noise?
What is your exhaust setup? Exhaust brake? A blocked muffler can make these sort of noises.
 

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Discussion Starter · #4 ·
Do you have a boost gauge, if so what is the boost pressure?
Any exhaust smoke when it is making the noise?
What is your exhaust setup? Exhaust brake? A blocked muffler can make these sort of noises.
I do have a boost gauge. There is a short video of it in my first post. I generally build a little over 20psi before the wastegate opens. I don't seem to have any trouble building and maintaining boost. The only time I get smoke is when I really hammer it, but even then the turbo spools up quickly and cleans it up. Just cruising down the road there is zero smoke. I'm running 3 inch straight pipe from the turbo back. No exhaust brake. I did have a muffler on it but removed it since the engine is louder than the exhaust anyway. Muffler or no muffler made no difference in the cab as far as noise goes. Also made no difference in the howling sound.
 

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Discussion Starter · #5 ·
I still have not been able to figure this out. Can't pinpoint where the noise is coming from seeing as I've already tried a boost leak test. I have notice a slight exhaust leak around the v band flange on the turbo, but I can't imagine that making the kind of noise I'm hearing. Does anyone make a good gasket to put in between the flanges to better seal the connection? Tightening the v band clamp did noting to help, so I'm assuming the surface(s) may be slightly warped.
 
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