Help identify strange noise at Highway speed

I need help identifying an odd noise that occurs at highway speeds (above about 2500 rpms). I would describe it as a repetitive whirling swoosh noise that picks up as rpms increase and then decreases to nothing as rpms slow.

A bit of context: the hole for the transfer case shifter is wide open because the truck was originally 2wd converted to 4wd and i haven't gotten around to modifying the hump to fit a shifter boot. Therefore any noise from road and drivetrain is quite noticeable. I had the motor rebuilt and after installing is when i noticed this noise start. prior to the engine swap i do not recall hearing this noise.

I am at a loss for what could be possibly causing this sound. Truck drives great. Engine running strong. Transmission shifts nicely.

It may also be pertinent information to mention that when i reinstalled the motor the already steep geometry of the front driveshaft was slightly shifted causing the drive shaft u joint to make contact with the transfer case support cross member and so i have the front driveshaft temporally removed. Could this noise be related to front axel or transfer case and made worse by removing the drive shaft?

If anybody has any ideas please let me know

Anybody?

Does anything change when put in neutral? A hole in the floor will amplify any noise.

Is it possible to capture the noise on a video. What you describe is unusual.

Put a boot over the hole first. There are a lot of normal drivetrain nosies that you don't hear.

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chief_shotts said:

Anybody?

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I got nothing but you did qualify for the axle Hall of Shame so that's cool.

What are the chances you changed engine mounts? Poly or steel mounts will make noises much more noticeable.

fast 99 said:

Does anything change when put in neutral? A hole in the floor will amplify any noise.

Is it possible to capture the noise on a video. What you describe is unusual.

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ill do my best to capture the noise on video but for now i am plagued with a no start condition. Back fire through the carb :/ ill be working on that for now.

Ricko1966 said:

What are the chances you changed engine mounts? Poly or steel mounts will make noises much more noticeable.

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engine mounts stayed the same. They are also fairly new.

I'm guessing driveshaft vibration or exhaust drone

Doesn't sound the same but a couple years ago I was driving down the road when I truck pulled along side of me. All the sudden I heard a loud noise I thought was a turbo winding up. I assumed it was the other vehicle and as the other vehicle passed by me I realized it was me. I pulled off real quick and the flywheel cover had come loose. Somehow I lost two of the bolts and part of it was slightly rubbing the flywheel.