Low rpm whine from rear. Differential?
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Cadillac STS Forum - 2005 through 2012 Discussion, Low rpm whine from rear. Differential? in Past Cadillac Vehicle Discussion; So, I usually drive around with music on, so I barely ever hear little noises that go on in or ...
  1. #1
    aliskerov is offline Cadillac Owners Fanatic
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    Low rpm whine from rear. Differential?

    So, I usually drive around with music on, so I barely ever hear little noises that go on in or around my car. Lately I've had to drive with no music, family trips and what not. What I've noticed is that the car has this slight whine in the low rpms on the throughway. It's pretty high pitched and not that loud, and it only happens when I step on the gas pedal (fades out instantly if I let off the gas), below 2.5k rpm. It kinda sounds like an alternator whine; it's hard to tell if it's coming from a side or from the center of the rear.

    I've recently done a differential fluid change (35k on the car). I replaced the fluid with a matching weight Lucas fluid. The lucas fluid mentioned not to add any additives, as it's LSD compatible. I'm wondering if it could be that the LSD in our cars requires a specific additive anyway. If that's the case then I'd just add it. Does anyone else have any ideas?

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    scott9001 is offline Cadillac Owners Fanatic
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    Re: Low rpm whine from rear. Differential?

    without me looking it up is this the not the same diff as in the cts's and they have a lot of problems with them i know they are getrag differentials and the cts has huge problems for this? is the vent clogged and building pressure in the rear end?

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    EChas3's Avatar
    EChas3 is offline Cadillac Owners Master
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    Re: Low rpm whine from rear. Differential?

    There was a recall for some bad seals in the early productionb runs. That and a less than robust mounting bushing seem to be the only common STS differential issues. I don't think it's the same diff as the CTS.

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    curtc's Avatar
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    Better not be the same diff as the CTS...My CTS was traded in howling like a banshee, don't really want that again...
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    aliskerov is offline Cadillac Owners Fanatic
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    Re: Low rpm whine from rear. Differential?

    I already replaced the bushing, so that's out. It's a faint whine, and one of my passangers even suggested that it might be a wheel hub. I just don't know how to diagnose either one. Riding up and down the freeway listening to noises is not a good way to find out whats wrong lol.

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    curtc's Avatar
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    Re: Low rpm whine from rear. Differential?

    If it's a wheel bearing it should change pitch/go away if you so do some nice slalom type turns....turn right and the noise goes away, then you know it's the passenger side bearing that's going bad as you just took the weight off of it, or vice versa.
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    EChas3's Avatar
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    Re: Low rpm whine from rear. Differential?

    Do you have a good dealer?

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    aliskerov is offline Cadillac Owners Fanatic
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    Re: Low rpm whine from rear. Differential?

    No idea, wouldn't trust one. I have a good mechanic, but the noise is so faint, that i'm sure it's impossible to tell whats wrong until it gets louder. I'm almost thinking that it may be as simple as a reverb caused by the stiffer poly bushing that I got from Creative Steel to replace the faulty stock differential bushing. The noise sounds like an alternator whine, but coming from the back. There's no grinding or other mechanical noises. It's a bit weird that it only happens when I step on the gas pedal, but thats when force builds up within the diff from the drivetrain. Sound reasonable?

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    curtc's Avatar
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    Re: Low rpm whine from rear. Differential?

    May need a shim for that bushing, CTS guys have run into that problem with the poly bushings...
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    Re: Low rpm whine from rear. Differential?

    hey guys new to the site but my 2005 sts does the same thing with the sounds from the rearend i hand a new reaened put in and it still does it now who has an idea... lol

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    scott9001 is offline Cadillac Owners Fanatic
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    Re: Low rpm whine from rear. Differential?

    get a mechanic to check out your wheel bearing on a hoist

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    aliskerov is offline Cadillac Owners Fanatic
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    Re: Low rpm whine from rear. Differential?

    I might have him take a look at the wheel hubs, though I doubt they'd go on a car with 35k miles on it. I'm thinkin it's a bushing, cause I changed the diff fluid a few weeks before doing the bushing, and I only noticed the noise after the bushing went in. If it's the case, I'd rather live with it as it faint rather then redo the bushing procedure lol;besides, I'd be hard pressed to think of a shim that wouldn't deteriorate away with time.

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    curtc's Avatar
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    Re: Low rpm whine from rear. Differential?

    Quote Originally Posted by aliskerov View Post
    I might have him take a look at the wheel hubs, though I doubt they'd go on a car with 35k miles on it. I'm thinkin it's a bushing, cause I changed the diff fluid a few weeks before doing the bushing, and I only noticed the noise after the bushing went in. If it's the case, I'd rather live with it as it faint rather then redo the bushing procedure lol;besides, I'd be hard pressed to think of a shim that wouldn't deteriorate away with time.
    Here's a CTS owner who installed new bushings, details their experience, including the use of shims.

    http://www.cadillacforums.com/forums...c-install.html
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    sztolcaddy is offline Cadillac Owners Member
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    Re: Low rpm whine from rear. Differential?

    In my STS I noticed like higher frequency whining from the rear at speeds around 40 mph and 1500-1700 rpm.
    It was like faint whining,so with music it's possible you won't hear it. They replaced rear differential assembly on GMPP
    and now the whine is gone. The total with no GMPP would be >$2500. Before I had replaced also motor mount and differential
    bushings. It was internal gear whine.

  16. #15
    buzz's Avatar
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    Re: Low rpm whine from rear. Differential?

    I am having the same problem. Unfortunately, I didn't see this thread before I created mine.

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