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C4S front differential/viscous coupling

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Just today, I noticed a strange noise coming from the front of my C4S. It sounded a little like a slipping belt - sort of a high pitched squealing. It only happnes under very specific circumstances, and it's intermittent. I've been able to replicate it a few times, but not consistently. The noise happens when I'm coasting down hill, in gear. I've only heard it in 3rd gear and 4th gear at this point. Giving the car gas when the noise is heard makes it stop entirely.

I'm beginning to wonder if the viscous coupling is "slipping", or if perhaps there's some other issue with the front differential. I had my differential fluid changed at the 90,000 mile service a few years ago, but it hasn't had any service or issues other than that.

Any thoughts? Does this sound like a differential or viscous coupling issue? I can already see dollar signs floating in front of my face...

I'll be taking the car to my mechanic to have it checked out, but I'd love to hear some opinions or hear about similar experiences and solutions.


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Maybe this is something else... I'm not sure. I've read several threads about the AOS making a squealing noise when failing. This noise does sound like it's coming from the front of the vehicle though, not the rear. I can't feel anything in the suspension or steering, I just hear the noise. It's strange...

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