Humming Rear Driver Side Only Around 70mph

optiontrader

109K, all stock.

Had similar issue on the opposite rear passenger side around 60K (yep, right after warranty expires), where it would start humming around 50mph. Thought tires - needed replacement anyways, but didn't fix. Dealer said bearing going bad - replaced; humming noise goes away.

Fast forward to now @109K, I've got a similar humming noise @70mph, but on the driver side. So I go “I know what this is” and go to replace the wheel hub assembly. However, while I'm underneath, I notice the black gunk on the diff. I don't think anything of it at the time - I finish replacing the wheel hub, but unlike the earlier problem on the passenger side - the humming is still there @70mph.

So I'm now thinking, the black gunk is from the axle, it's definitely on the drivers side rear so I purchase a replacement (reman) axle to slap on.

But searching thru the forum, the black gunk is most likely coming from the differential bushing.

So my question (axle's off right now): could the diff bushing cause this humming, and only around 70mph? There are no clunks or other noises that I can hear.

Insight, oh 370Z gurus?

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