Wierd Noise in the Rear

Looking for some input on what this noise could be.
The noise is coming from the rear end. Hard to describe it, almost like a cyclic rumble/growl that increases with speed. Sounds very much like increased road noise. There doesn't seem to be any play on the rear tires so the bearings should be good (I put in new rear wheel bearings last year).

Something tells me it's coming from the rear differential so I drained the fluid and put in MotoMaster synthetic 75w90 but there was no difference in the noise.

It's not incredibly loud, but definately noticeable with the radio off. I can't really hear it until about 60km/h.

Anyone have any ideas?

maybe it's your driveshaft

is it like a "howling" noise?
like an airplane is flying above/around you?

Bad rear CV joints.
Bad U-joint in driveshaft.
Poor gearmesh in rear diff.
Bad bearings in rear diff.

Yea, I guess the sound can be seen as a howling sound. The sound can be best described as wind blowing into a hollow area...so yea, I guess thats a howling sound.

Nick, thanks for the info. I'll check the CV joints and the U-joint when I jack up the car tonight. Hopefully some good old grease will provide a temp fix since the holiday season hasn't exactly left me a rich man...*crosses fingers*

Anyway I can check the bearings and gears in the rear diff without pulling it apart?

You can check for EXTREME play in the input shaft bearings by tugging on the flage. For small play and the others, you need to open it up.

Well, I jacked up the car during lunch to check for any extreme play and didn't find any. Power-washed all the grime off under the car and gave'er a good greasin but the sound remains...somehow I didn't think it was going to be that easy...

Any way to know for sure if the boots still have grease in them or if they've dried out?

Also, is checking for lateral play on the tires the best way to check on the wheel bearings? A friend of mine is convinced that replacing my 1 yr old rear bearings is the way to go. I'd rather not have to go through the pain of getting those bearings off again...I think getting a root canal would be more pleasant...

If they were replaced a year ago, greased properly and they don't wobble, then they're probably fine.

A well tuned ear would be the best tool to narrow down the source of the sound.

You can use mine if you get the car down here.

Sweet. Thanks for the offer Nick! Don't suppose you have some spare time for me to head down this weekend?

Anytime that's good for you is good with me.

I'm sure i can spare a little time for a quick drive.

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