Low, faint oscillation

[jeedee]

(Didn't know where else to post this, and a search didn't exactly enlighten me).
Have a repeating faint oscillation, most prominent at 55 mph, starts at about 50/51 mph....ends at about 59/60 mph. No vibration anywhere, just the low sound. Seems less with foot off accelerator, and coasting in neutral. The oscillation never changes speed with RPM's. No U-joint/drive shaft noise. Haven't been under there to check....midwest winters aren't conducive to under-vehicle work.(Recently purchased).
Appreciate any suggestions.
2002 XLT 4 door 2WD auto/3.0 posi rear 86K.
thanx, Charlie

 

[RonD]

Reads like wind noise
Anything recently added to exterior?
You can test if its wind noise on the next windy day, drive into the wind and see if noise starts sooner, or with the wind and see if it starts later.

 

[doorgunner]

fluid low/needs changing in differential???

 

[alwaysFlOoReD]

A long time ago I added a side gear shim to a 9" rear to get a cheap posi. In the process I changed the mesh tooth pattern and ended up with a sound like you're describing. When I removed the ring gear and put it back in, I was a tooth or two out from the original way the ring gear teeth meshed with the pinion gear teeth.
Perhaps if work was done to the rear.....
Also I could see a sound like you're describing from slightly different sized or make tire on the same axle.

Richard

 

[hopster]

that sounds to me like a wheel speed vibration. so you can narrow it down to anything that turns at the same rpm as the wheels. tire/wheel, axle shaft, brake drum/rotor, etc.

 

[jeedee]

Thanx for all the input folks.