I've been trying to figure this out for awhile and cannot seem to nail it down.
The noise comes from the engine bay, almost certainly the passenger side.
It only happens (noticeably) above about 50, maybe 55, miles per hour.
It only happens under load and goes away when I back off the throttle even just to maintain speed. ANY throttle makes the noise appear. Removing throttle at all makes it go away.
If I drive on the highway with cruise control on the noise appears going up even the slightest grade and goes away as soon as the road is flat again. It is very sensitive!
Now the fun part, internet sound charades!
The best way I can describe the noise is almost like someone sitting in the engine bay while I'm driving, sucking through the straw of an empty cup. That gurgling noise...but muffled. It also kind of sounds like a high-speed bearing with no lubrication when they get that "rattly" kind of sound. Skip to 1:40 in the following video to get an idea of what I mean...when he spins the bearing by hand. Also, that video is kind of fun...sorry to those of you who end up on a 2-hour Youtube binge after watching that! The noise does not sound like an actual sucking sound like a vacuum leak, it is more mechanical but very inconsistent...coming and going in spurts as long as the throttle is pressed. It also doesn't sound as distinct as a failing bearing. It is a strange sound that I can only relate to those things for lack of a better description. It isn't loud enough to record and post for you to hear either. Sorry that conveying the sound isn't easier...I just know something is going to fail eventually and probably leave me stranded in the desert.
https://www.youtube.com/watch?v=BN7ATpnGQW0Now, some things to consider. The turbo is NOT OEM. I didn't realize it when I bought it, but it is obviously a no-name turbo. There are only a few markings on it to identify it and I have not tried. The shaft seems like it is in good shape and the vehicle has made this noise since I bought it at 88k miles. It has 115k now. If the turbo were failing it would have done it by now. I'm not saying it ISN'T the turbo, but it doesn't seem like a failing component if it is. Is there anything else in/on the turbo that might make this noise. even if the turbo is generally healthy? A seal that is leaking at 55+ mph for some reason? Could the vacuum solenoid or modulator make any sounds at higher speeds? I just rebuilt the top end from the head gasket up. I was thinking I would find the problem somewhere along the way and be able to eliminate it, but it is back now that things are back together. EVERYTHING has a new gasket, most of them with high temp RTV or copper-coat gasket sealant. I can't see or hear any leaks (or see evidence of any) of any kind under the hood. CAC hoses, air box to turbo hose, CCV to turbo, etc, are all well clamped and sealed from what I can tell. I re-seated the EGR end-cap on the exhaust manifold with a generous amount of high temp RTV as well, while it was off. Injectors are not leaking. I can't think of anything else in that area that might make this noise!
Does anyone have any ideas of how I could start eliminating possibilities without throwing tons of money at replacing random parts until I find it (possibly including the turbo)??? I obviously have no way to get under the hood at 55 mph to locate it under load when it seems to be making noise. Any help would be appreciated. If I don't find it soon I'm going to wrap the Jeep around a tree and call it "fixed"! haha!