I get a weird humming/whining/harmonic noise that slowly fades in at around 40mph and fades out around 45mph. If you totally let off the gas coasting at the speed range it's most audible it goes right away and comes back as soon as the slightest amount of gas is applied. Shifting into neutral at the speed it's most audible also makes it go away.

Transmission shifts nice and smooth and there's no noticeable slipping or vibrations, everything "feels" good otherwise - just this very annoying and very audible harmonic noise. Any idea's what could be causing this? This is a 04 Lightning with now 16,000 miles on the clock that replaced my wrecked 03 and my 03 was perfectly sound at all speeds.

 

check the balance of the drive shaft. that or your getting gear noise from all of the friction modifyer burning up in the differential. but id check the drive shaft first. one way to see if its in the engine or drive line run it up to that speed and drop it to neutral let it cost back down. but its likely driveline related.

 

When mine started doing thta at 12k it turned out to be in the rear end. Had pinion gears replaced under warranty. So far, so good, but I have only put 6k miles on since.

 

I had a similar problem at 60k in my truck, turned out to be the pinion bearings.

 

yah my rear end has been rebuilt 3 times because of that rear end noise. but if u drop it into neutral and dont feel the vibration anymore its in the drive line. not the engine.

 

Ya I took a local transmission mechanic for a drive today and he said it sounded like pinion gear/bearings. He's gonna put it on a lift tomorrow at noon find out exactly what's wrong at no charge.