Bad Transfer Case or Rear Differential

Looks like my truck is starting to break down after all these years. I need help on figuring out a noise issue with my truck.

Symptom:

• High pitched noise (jet engine sounding) once you get to 35 MPH and up. Noise will be more noticeable at higher speeds. Pressing clutch or putting car in neutral will not help.

Things already Replaced:

• Transfer case, transmission, and rear differential fluid with Mobil 1 Synthetic Gear Lube.
• Center support bearing
• Both rear wheel bearing and seals

Could it be the transfer case? Rear differential? Any help/suggestions would be appreciated. Thanks

 

I'm no expert but I don't see how it could be the t-case if you arent in 4wd. Does it sound like it's coming from the rear? The t-case pretty much right below the driver.

Does the sound get louder the faster you go or stay the same?

 

Okay thanks for the suggestion for possibly eliminating the t-case as the cause. It sounds like its coming either in the middle or the rear of the truck; it's difficult to pin point. I plan on putting a camera on various locations and see if I can capture noisier spots on video.

The noise gets louder with speed.

 

Probably the 3rd member. Put it in jack stands and throw it in second gear