: Vibration / noise at certain RPM



av8erdunn
06-20-13, 08:47 AM
I have started to get a vibration and a humming sound that starts at about 2100RPM. It doesnt follow speed I dont think because it does it in any gear. Its odd because if I am cruising at 75 around 2300-2500 RPM it will constantly do it until I let of the thottle; then it quits. But once I apply throttle again it starts right back. Its like under a loaded condition is the only time it happens. It gradually gets louder and a little worse vibration as RPM increases but I think it finally gets to a certain frequency then it just maintains that frequency.
Any ideas?

JFensty
06-20-13, 08:58 AM
Do you have the stock clutch? Any mods? Stock mounts?

av8erdunn
06-20-13, 09:17 AM
Its the stock clutch, and my motor mounts were just replaced with new OEM mounts. Only mods are a corsa exhaust coupled to Kooks headers and cats and a custom tune.

rand49er
06-20-13, 09:33 AM
I was thinking mounts, too, until I saw that last post.

If it's not exhaust related (where the flow is related to load or throttle position but doesn't fit the "vibration" described above), I'm wondering what else it could be if it's not related to anything downstream of the flywheel (since it "doesn't follow speed").

Anybody else?

Cadillac Cust Svc
06-20-13, 12:17 PM
I have started to get a vibration and a humming sound that starts at about 2100RPM. It doesnt follow speed I dont think because it does it in any gear. Its odd because if I am cruising at 75 around 2300-2500 RPM it will constantly do it until I let of the thottle; then it quits. But once I apply throttle again it starts right back. Its like under a loaded condition is the only time it happens. It gradually gets louder and a little worse vibration as RPM increases but I think it finally gets to a certain frequency then it just maintains that frequency.
Any ideas?

Hello av8erdunn,

I see you have gotten some advice from other members on here. Have you been able to find the cause of this vibration and humming sound? If you want to further discuss your concern and are thinking about taking it in for a diagnosis, private message me so we can continue our interaction.

Sincerely,

Laura M.
Cadillac Customer Service

LS6Steve
06-20-13, 02:49 PM
Have you checked your transmission mount?

av8erdunn
06-20-13, 03:32 PM
I have not looked at it but I have had a bad transmission mount before and i could punch the throttle and let off quickly and I would get a BANG, this one didnt do that. I will look this afternoon though.

LS6Steve
06-20-13, 03:50 PM
I've had cars do that too, but usually more so when there is a ripped top-mount type. With these bottom mount ones, the seem to fail differently. i just replaced a bad one and it sounded IDENTICAL to a bad input bearing issue, there was a knock with every input shaft RPM. Now it's gone, smooth as butter.

darkman
06-20-13, 04:15 PM
...a humming sound that starts at about 2100RPM. It doesnt follow speed I dont think because it does it in any gear. Its odd because if I am cruising at 75 around 2300-2500 RPM it will constantly do it until I let of the thottle; then it quits. But once I apply throttle again it starts right back.

These quoted words, viewed alone, would be a description of the infamous differential whine. Whether it is a "whine" or a "hum" could be a matter of semantics. The differential whine can be initiated and ended with light on/off application of throttle particularly at cruising speeds.

rand49er
06-20-13, 06:17 PM
OP, is the sound coming from the motor area or from the rear end? Can you tell?

As darkman points out, a "whining" sound would indicate your diff. Mine whines/hums a bit, but doesn't vibrate.

ImEpayne
06-20-13, 07:14 PM
I've got the same issue in my '06. mine is definitely a vibration at the same rpm's regardless of speed. Now I know I need to do my Harmonic Balancer. I've been under the assumption that this is the cause of the vibration.

Let us know what you figure out.

av8erdunn
06-20-13, 07:34 PM
Can't really tell where its coming from. If it was diff whine, would it have not been there in the morning but there in the afternoon? Would it also cause a vibration? But then again it was doing it at the same rpm in second as it was in fifth. Very odd!!!!!!

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I've got the same issue in my '06. mine is definitely a vibration at the same rpm's regardless of speed. Now I know I need to do my Harmonic Balancer. I've been under the assumption that this is the cause of the vibration.

Let us know what you figure out.


How do you know you need to change your harmonic balanced?

darkman
06-20-13, 07:49 PM
The differential whine is not accompanied by vibration. If the issue varies with engine rpm as opposed to road speed, it presumably is an issue upstream of the transmission.

Heavybody
06-20-13, 09:14 PM
Mine has a similar whine issue ... Fold down the rear seat or armrest to make sure the whine or hum is the diff it should be much louder and noticeably from the rear of the car. I ignore the noise as I assume it's the notorious whine... Or normal...lol


Good luck with the vibration I had one similar to what you describe and when I replaced my tires it went away almost all the time... (It was so bad I avoided highways for quite some time) rebalancing your wheels is a possible inexpensive solution if you have some miles on your tires...

When the vibration does come back I can usually down shift to 5th or play with the throttle to get the drivetrain to adjust to a smooth place again. Not sure of a solution yet as I haven't had much time to address the issue but I have found ways to make it tolerable

Keep us posted!

Cadillac Cust Svc
06-20-13, 09:19 PM
I've got the same issue in my '06. mine is definitely a vibration at the same rpm's regardless of speed. Now I know I need to do my Harmonic Balancer. I've been under the assumption that this is the cause of the vibration.

Let us know what you figure out.
Hello ImEpayne,

I apologize that you are experiencing the same issue with your CTS-V. Have you taken your vehicle to the dealership to have it diagnosed? If you would like our assistance in working with the dealership as well regarding this issue, please private message us. Thank you very much for taking the time to read my post.

Gregory W.
Cadillac Customer Care

ImEpayne
06-21-13, 02:07 PM
I was told by the techs at the dealership that I work at. Though it is a Nissan dealership so I suppose there could be some error. But, after all the posts I've read about the harmonic balancers i think it is a fair assumption.