Speed Dependent Whine Under Acceleration (pic hvy)

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Sep 30, 2019
I have a whine that sounds similar to a mans voice if he was singing at his highest pitch. The sound appears under heavy acceleration; top of 1st gear and top of 3rd when going uphill. The whine fades in, increases in intensity until its peak, and then fades out again. The heavier the acceleration, the more pronounced the whine.

There is also a slight rumbling that appears around 45-50mph. It is present regardless of acceleration, or really anything else and is very consistent. The rumbling doesn't shake anything inside the vehicle but does shake the side mirrors enough that I cant make out what sort of car is about to pass me. It do suspect the tires..

Visual of the sound's presence:

Trans Position ~~~~
Miles per hour~~~~~[5-10-15-20-25--30--35-40-45---50----55---60----65-------70--------75------80]
Whine Intensity~~~~(_...--==|||==--...______...--==|||||||||||==--...___________________________)
Tone Freq (Hz) ~~~~{--375-400-425-450--------550-575-600-625-650-675----------------------------}
Rumble Presence~~~~:_______________.........-----------.........._______________________________:

The sound began after I went off-roading. I didnt use 4WD and so had a couple abrupt wheel spin stops, nothing too crazy. I remembered this and checked the rear differential, this is what I found:

Drain Plug Magnet
Those are not shavings. Its the metal paste formed into what looks like shavings by the magnet.
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It was hard to get a shot of the pinion.
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The oil is actually not as dark as it looks. The rear diff is limited slip and I think its dark because of clutch material. It smelled like a dying transmission. I could smell the oil the instant the plug broke loose, before unscrewing it!

I went ahead and did the front diff also. The oil up there was a lot darker but didnt smell bad.

So, to me, the rear diff looked OK and from what I've read this could also be a transmission issue or a transfer case issue.

The whine is still present after the diff oil change, not that changing the oil would undo damage done in its internals. Does the rear diff appear to be damaged? I dont know if what im looking at is pristine or junk..

Also, what can I do to track down the source of the whine?
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Its a 1999 Nissan Pathfinder, H23B rear diff. Im using what the FSM calls for which is 80w90.
I will ask someone with the same diff to take a temp reading on the outside of the housing in the area where the bearing race seats. I hope that's not what it is.. I don't have any experience at all with setting up a differential.

The ujoints feel solid, however I do have replacements on hand. It wouldn't hurt to go ahead and change them. The set that are on there now are NSK and have likely been there since the vehicle was a dealership trade-in 150k miles ago.
For the whine:

if its present in one gear and not another, that eliminates the diff. I would look at the power flow through the transmission, what component is engaged in both 1st and 3rd but not 2nd or OD?

For the rumble / vibration ... agree check u joints and tires.
This issue turned out to be tires. Temps dropped here in north GA and the pressure in my tires followed suit.

The shaking/rumbling I think actually is the front driveshaft ujoints. Thank you PimTac
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