You said you've had this noise from day 1, then you said you've had it since the HX35. Has it had the HX35 since day 1? Just trying to get this straight.

 

 

Oh, I see. I misunderstood. Hopefully someone else comes through, because this makes no sense to me at all.

 

That sound clip would help. Because I , like many others that have read your post, don't know what sound you're chasing. Could be something simple. Could be something huge.

Considering all of the changes that you have made to the tuck and it still has the sound. I would start with a compression and a leak down test. Just to eliminate a base engine issue. Its also possible that you have an injection pump issue. But there's no way to tell without hearing it ourselves.

While I don't see this being it, have you ever verified the timing on the truck? I've seen timing do funky things.

 

 

 

 

Mine sounds like that until it warms up, Are you still on stock governor springs? if so changing to 3k springs will help.
What do you idle at?

 

I did some thinking, that fluttering sound is the interaction of your exhaust gas with the turbine wheel, at cold start my truck idles at 400 rpm, exhaust flow is not great enough to accelerate the turbo to a sufficient speed where it doesn't disturb exhaust flow, but as the engine warm up the exhaust drive pressure increases speeding up the turbo to a point where it doesn't impede exhaust flow and just sounds smooth with a nice whistle.. Thats why no matter what turbo you put on there that 12 valve will do that. Mine did it with a HX35 and does it with a Cheetah.

Try jamming something in the turbo to prevent it from spinning and see if the sound is still there. No amount of drive pressure will over come a piece of metal holding it static.

TLR

nothings wrong with your truck, its a completely mechanical turbo diesel and its normal with no temperature or barometric pressure compensation. stop worrying and drive it.

Just so you dont think I'm bullshitting, I'm a jet engine mechanic, turbo's are my life, knowing how this stuff works and interacts is my job(I made an account just to type in this thread)... I thought about this for awhile before posting. The other trucks you hear are probably have a high idle, my Idle is set to 750 RPM AC off.