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Lately I've noticed a loud drone coming from my 1999 996 6-speed when cruising down the road. It sounds a whole lot like when the rear differential bearing went bad on my old Mustang, but I'm not quite sure if the 996 has the same kind of differential.

I'm fairly certain it's not just wheel bearings because there's no change in tone as I steer the car from side to side.

I was kind of ignoring the problem, but I had the car in for an AOS replacement and the shop mentioned I have a "noisy transmission." Is the differential in the transmission?

I have shop manuals, and I'll order the parts to swap the bearings out, but I'm just not really sure what I need to be replacing.

Thanks for any help.

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Go neutral from second gear rolling. If the noise carries over then it is not the tranny. The differential should not be in the "tranny" it just has gears, rods and selectors in it. Then you need to run a series of tests to determine where the noise is coming from. Rev in neutral; accellerate quickly; accellerate slowly(in 1st gear to 6krpm and down) same in second, Does the noise vary with rpm's? does it vary with speed? I know the droning noise in my experience is from bearings but your idea of droning may be different than mine. Miles/maintenance could help folks here.

For clarification, some people call everything including the bell housing the tranny. I refer to the tranny as the gearbox only.

Edited by ViolaGT3
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It could be the transmission. I had to replace mine in a 1999 C4 at 117K and it had become noisy in ways you describe it. Before I had the tranny replaced, I had the differential oil changed. That made no perceptible improvement. But as mentioned above, it could be other issues. How many miles are on your tranny, and how regularly has the tranny fluid been chanced? Maintenance lists calls for a change ever 80K. I wouldn't do it less often than 60K, and I don't track my car.

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The pitch varies a little with speed and it disappears when I clutch.

Well, Well, Well. I would put my wooden nickel on the throw out bearing.

With car running have someone listen carefully by the rear tire depress clutch, hold, release, repeat. you should be able to hear what is definately called a "droning" noise while clutch is released.

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I would suggest that it might be the pinion bearing (which is a sealed bearing known to wear) or planetary gears. I had a similar issue - speed sensitive whine from just behind the driver's seat (worse in gears 4 to 6).

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Just had the exact problem on my '00 996 with 110k kilometres. In the end I needed a tranny rebuild. The OEM bearings are crap, supposed to be sealed but grease leaks out over time with heat and pressure. The whine is the ball bearings banging around in the dry bearings. While I was in there I had the RMS and IMS bearing done as well. Pricey but worth it, no worries now!

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I hope it's not anything major, but you might try jackstanding the rear end and running her through a few gears checking the housings with a stethescope.

Our 11' Outback has a noisy tranny, my Porsche doesn't.

Also a fluid change could tell you alot.

Edited by ViolaGT3
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Hmmm. All I can say for certain is it's a bearing somewhere. It's definitely a bearing whine. Guess I'll have to put it on blocks and find a helper, so I can see if I can track the noise.

I did a transmission fluid change somewhere around 85k miles. I'm about to break 150k though, so I guess I'm probably about due again.

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Hmmm. All I can say for certain is it's a bearing somewhere. It's definitely a bearing whine. Guess I'll have to put it on blocks and find a helper, so I can see if I can track the noise.

I did a transmission fluid change somewhere around 85k miles. I'm about to break 150k though, so I guess I'm probably about due again.

Wow that's impressive I hope I see that many miles out of mine! Although the odds aren't in my favor a 2kmls. per year. Just @ 80k now. bought it with 60k about ten years ago. Make sure you post your findings, but I chance to say with that many miles it may verywell be time for a rebuild/replace.

Edited by ViolaGT3
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  • 1 month later...

When I'm running about 80mph on the freeway in 6th gear it whines like crazy! That's when it's most pronounced. I think I'm going to have to take it to the dealership for an official diagnosis.

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  • 5 years later...

Did this ever get a resolution? I am in the same boat. A noisy whining that is worst between 40-60mph in 4-6 gear. Pushing the clutch reduces the whine a lot, but not eliminated. My car is a 1999 996 C4.

A mechanic nearby has suggested differential side bearings.

 

Can anyone recommend a shop that can repair these in the Bay Area? I can R&R the transmission myself, but I am not sure I want to get involved with shimming bearings to adjust the backlash or preload.

Edited by SpawnyWhippet
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