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Discussion Starter #1
I've come into work the last few days with the windows up, and while freeway cruising or light acceleration, I hear an oscillating sound from the back of the car. it stops if I accelerate hard or let off the gas. Can't hear it windows down or music going, but no mistaking it windows up stereo off. It's not a whine, more of what would be a tire sound on rain grooves. It diminishes somewhat once fully warmed up.

Thinking I'll throw some fresh fluid in the diff (I just hit 3000 miles). Anyone else notice this or any other ideas what this might be?

Thanks,

Mark
 

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I personally wouldn't do anything like replace the diff fluid on a car with 3000 miles on it. That's a straight up warranty issue... Unless you give them a reason to not cover it... Like changing the fluid. Take it to the dealer and let them document and recommend a course of action.
 

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I personally wouldn't do anything like replace the diff fluid on a car with 3000 miles on it. That's a straight up warranty issue... Unless you give them a reason to not cover it... Like changing the fluid. Take it to the dealer and let them document and recommend a course of action.
While I agree that this is a dealer issue and that the owner should get any issues covered under warranty, I also don't think we should be making people fearful of maintaining their own vehicles under warranty. Changing the fluid is not a valid, rational, or likely reason for a dealer to refuse coverage, especially when the differential only takes your basic 75W-90 GL-5 gear oil and not some special friction modified gear oil.
 

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Discussion Starter #5
My reflex to replace this fluid is due to the NC Miata and known issues with how they filled the differentials incorrectly. Pretty sure this is the same differential. The thought of having the rear-end torn apart makes me more uneasy than spending the $15 for some fresh fluid.

Warranty issues aside, anyone heard of such a noise and impact of good clean fluid? I did some googling on this and lots of people did have results with good fluid on various other noises.

Thanks for the input.

Mark
 

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If you're having trouble with the differential at 3,000 miles, take it to the dealer and let them sort it out under the warranty. Even if it's just low on oil, it's their problem not yours.

Change the oil if you want to, that's not the issue. If there's something wrong, though, let the dealer fix it. It shouldn't be your problem.
 

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My reflex to replace this fluid is due to the NC Miata and known issues with how they filled the differentials incorrectly. Pretty sure this is the same differential. The thought of having the rear-end torn apart makes me more uneasy than spending the $15 for some fresh fluid.

Warranty issues aside, anyone heard of such a noise and impact of good clean fluid? I did some googling on this and lots of people did have results with good fluid on various other noises.

Thanks for the input.

Mark
I wouldn't want my car torn apart either.

I haven't heard of such a noise. Can you elaborate on the known issues regarding the NC Miata and the differential fills?

I'll be changing my fluids (engine, trans, diff) here in the next month or so.
 

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If you're having trouble with the differential at 3,000 miles, take it to the dealer and let them sort it out under the warranty. Even if it's just low on oil, it's their problem not yours.

Change the oil if you want to, that's not the issue. If there's something wrong, though, let the dealer fix it. It shouldn't be your problem.
One reason why I opted for the Lusso rather than the Abarth was the LDS. My Solstice had one, started making noises and when I took it in it turned out that GM had put out a service bulletin to replace the differential. (Which the dealer did, no questions asked even though it was well out of warranty). It turned out that the part came from another GM product and would occasionally lock-up while being driven, causing accidents. There was no recall, you just had to mention noises when you brought it in so I'm assuming there are plenty of faulty Solstices out there. That's always bothered me. So, since I had no plans to drive my 124 on a track, I was just as happy to have the simpler unit. Fewer potential issues in my mind. I know its a different manufacturer but just couldn't get that issue out of my mind.
 

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Haven't read yet if the audio frequency changes with speed or not.
 

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I'm sorry you had trouble with your Solstice, but I think GM is a bad car company in many ways. I had a LSD in my Miata that was in fine working order after 16 years. I expect no issues with the one in my Abarth, and it's extra fun every time I drive it.
I think this is very much an "apples to oranges" comparison.
Best regards
Pete
 

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While I agree that this is a dealer issue and that the owner should get any issues covered under warranty, I also don't think we should be making people fearful of maintaining their own vehicles under warranty. Changing the fluid is not a valid, rational, or likely reason for a dealer to refuse coverage, especially when the differential only takes your basic 75W-90 GL-5 gear oil and not some special friction modified gear oil.
I agree that changing the fluid probably would not and certainly should not cause a denial of warranty claim. But I stand by my statement that at 3,000 miles, this should be entirely a dealer issue. I don't believe the rear diff should need to be "maintained" at this point in it's life... But, as my statement said, this is what I would do (or not do). Everybody has their own ideas, I just threw my 2 cents in the mix...
 

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One reason why I opted for the Lusso rather than the Abarth was the LDS. My Solstice had one, started making noises and when I took it in it turned out that GM had put out a service bulletin to replace the differential. (Which the dealer did, no questions asked even though it was well out of warranty). It turned out that the part came from another GM product and would occasionally lock-up while being driven, causing accidents. There was no recall, you just had to mention noises when you brought it in so I'm assuming there are plenty of faulty Solstices out there. That's always bothered me. So, since I had no plans to drive my 124 on a track, I was just as happy to have the simpler unit. Fewer potential issues in my mind. I know its a different manufacturer but just couldn't get that issue out of my mind.
I did some research on this one before I bought it and found that it used a helical type differential, which functions entirely on mechanical parts as opposed to some of GM's differentials, which use clutch packs that are sensitive to the friction properties of oil. One of my friends had his differential replaced twice last year on his Camaro SS due to rear end noise. Due to more moving parts, helical limited slip differentials tend to be slightly more taxing on the oil, but this is really a non-issue given the availability of high quality synthetic lubricants on the market and the fact that the differential takes less than a quart of oil to fill.

I agree that changing the fluid probably would not and certainly should not cause a denial of warranty claim. But I stand by my statement that at 3,000 miles, this should be entirely a dealer issue. I don't believe the rear diff should need to be "maintained" at this point in it's life... But, as my statement said, this is what I would do (or not do). Everybody has their own ideas, I just threw my 2 cents in the mix...
I agree with you on that statement, I just want to be cautious not to deter people from servicing their own vehicles, with their own choice of lubricants, during their warranty period.
 

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Discussion Starter #13
Coming home tonight found that with speed it varied, but much over 70 too loud to hear. 60-65 at light acceleration I can hear it. Sounds like a 4 wheeler with big tires. Any foot movement stops it but steady state it is there. I have very sensitive ears and guessing most wouldn't hear this but will get it checked soon. It's subtle and windows down, music on or even talking and you can't hear it. If it wasn't oscillating I'd consider normal car sound. Not a whine at all, more of a wawawawawawa low frequency.
 

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Discussion Starter #14
Regarding the nc diff issue, many were filled with too much cutting compound and if not changed got noisy. Mazda issued a tsb and replaced any that were noisy. Changed the fluid on my '13 at a couple thousand miles and it was nasty. Filled with clean oil and it didn't make a peep.
 

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Discussion Starter #15
Put in new fluid, Lucas oil 75-90. Took maybe 8 minutes no jack just a piece of cardboard to lie on. Already had the harbor freight pump and 23/24mm socket needed. Oil dark black and stinky but was full. The magnetic drain plug had about 2mm of sludge on it. Cleaned it up, pumped in new oil and took a drive. Not surprised but zero change. With volume even slightly up beyond zero and windows up can't hear it but with nothing in background it's there. A buddy has an abarth so time to check his out and if quieter will call the local dealer. My bet is they will say they hear nothing but worth documenting.

And as diy projects go this is the easiest and I feel better knowing the sludge is out and it's nice and clean. And I brought some office work home, so perhaps some procrastination involved ��
 

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I'm betting the noise is normal. Diffs get noisy. You should hear the Hellcat diff in my 2012 Challenger.
 

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Are you sure it's the diff and not a tire?
 

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Discussion Starter #18
Are you sure it's the diff and not a tire?
that was my first thought, checked pressure all around and all good. inspected tires for any nails, etc and see nothing. The fact that it stops when I let my foot off the pedal kind of ruled that one out in my mind.
 

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that was my first thought, checked pressure all around and all good. inspected tires for any nails, etc and see nothing. The fact that it stops when I let my foot off the pedal kind of ruled that one out in my mind.
I would tend to agree, but tires can do some bizarre things. I think I'd probably rotate the rears to the front, just to be sure. It'll be a good opportunity to inspect the suspension for tightness, anything rubbing, or any other oddities, as well as just look at the diff to see if there is something which doesn't look right (oil, stains, etc).
 

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This is a real tricky one. But if the problem only now arose and was fine earlier, I can't see it being the tires. Especially because it's just noise and no feel
 
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