: Low rpm whine from rear. Differential?



aliskerov
06-03-12, 05:01 PM
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?

scott9001
06-03-12, 08:22 PM
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?

EChas3
06-03-12, 08:48 PM
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.

curtc
06-03-12, 09:21 PM
Better not be the same diff as the CTS...My CTS was traded in howling like a banshee, don't really want that again...

aliskerov
06-04-12, 12:26 AM
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.

curtc
06-04-12, 12:45 AM
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.

EChas3
06-04-12, 10:48 PM
Do you have a good dealer?

aliskerov
06-06-12, 12:30 AM
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?

curtc
06-06-12, 12:35 AM
May need a shim for that bushing, CTS guys have run into that problem with the poly bushings...

LaidBackLux
06-07-12, 07:04 AM
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

scott9001
06-07-12, 06:42 PM
get a mechanic to check out your wheel bearing on a hoist

aliskerov
06-07-12, 07:54 PM
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.

curtc
06-07-12, 09:07 PM
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/cadillac-cts-first-generation-forum-2003/250678-revshift-drive-shaft-coupler-disc-install.html

sztolcaddy
06-24-12, 10:01 PM
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.

buzz
06-25-12, 09:26 PM
I am having the same problem. Unfortunately, I didn't see this thread before I created mine.

silverfox05
06-26-12, 07:32 PM
mine started a couple of weeks ago. more like a low growl/hum. not as pronounced,the faster i go. scared to take it in. just had trans rebuilt last
year, just before warranty expired.

buzz
06-27-12, 10:14 PM
I notice at certain speeds and throttle positions, I can hear a slight whine. It is fairly high pitched, and I might think it was coming from the radio. I can hear the sound whether the radio is on or off, so I doubt it is the sound system. Anyway, it appears between 40-55 mph, and seems slightly related to throttle position; i.e., whether engine is pulling or coasting. I know if I hear the sound, and let up on the throttle, it goes away; however, it doesn't always reappear when I begin accelerating again. It is intermittent and that type of condition is the most difficult to diagnose.

It might be nothing to worry about, and if I had been driving the car for the past 30m miles, and the noise was always there, I would just consider it a bother and nothing more. Unfortunately, as of today, I added @ 5m miles, so the noise is new. I believe I read somewhere the center diff can make this type of sound, I am just wondering if anyone else had a similar experience. The 2008 STS is a V6 with the all-wheel drive feature.

buzz
06-27-12, 10:21 PM
Related to this, I was having lunch today with a couple of old friends. One of my friends has a 2005 Ford 500 with AWD. He said he was noticing a slight whine at speeds between 40 - 60 mph! He described the problem almost exactly as I did in my previous post. He got my attention and it appears this is more common than I thought. He has 150M on his 2005 AWD Ford 500, and I have only 68M on my 2008 STS. I am wondering if this is covered by Cadillac's drive train warranty? I am going to check the owner's manual to see if I have any warranty left. I do know I am good to 120M for the timing chains; however, this is different.

aliskerov
06-27-12, 11:16 PM
well, mine is high-pitched, and it does almost sound like alternator whine. I'm just going to live with it. No warranty on the car and I just did the diff service and poly bushing. I usually have the music on anyway, and since I also have an exhaust I can dilute the noise with a little throttle power :D I doubt a mechanic could point out such a faint problem which is hard to recreate in a shop. If anyone else is up for it, I'd love to hear the results of a visit to a mechanic. Cheers.

buzz
06-28-12, 01:25 PM
Well, I am going to discuss this with a GM service tech. I discovered last night the drivetrain warranty is 5 years or 100M miles, so given the original delivery date for my STS was November, 2007, my drivetrain warranty is good untll November 2012 or 100M miles, whichever comes first. My only concern is how GM defines a failure. Is it a noise indicating something is not right, as with the failure of my 2006 SRX timing chain; or, is it a complete failure of the drivetrain where I need to tow the vehicle in for service? I will let you know what I find after a visit to the dealer.

EChas3
06-29-12, 11:30 PM
I hear some noise once in a while. I figure it's reasonable to expect a few noises from a car with 75,000 miles that was built seven years ago.

If it ain't broke, good luck.

buzz
07-02-12, 09:04 PM
I hear some noise once in a while. I figure it's reasonable to expect a few noises from a car with 75,000 miles that was built seven years ago.

I agree, Chas; however, this whine is an indication something in the drivetrain is not quite right. I purchased and received the 5 volume GM service manual just today. I purchased service manuals before, and they have saved me $$ whether I do the repair myself, or leave it to a trusted service center (dealer). I looked up the transfer case and the second symptom listed is "Transfer Case Whine or Rumble Noise". The likely Cause, "Faulty bearings" or "Worn or loose chain".

My car is still under warranty; at least for the drivetrain, so I will be visiting a dealer sometime in the near future. I will let everyone know how it comes out.