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Discussion Starter #1
Hey folks Im having 2 issues. I just bought my V last week and it seems that it has a vibration at all highway speeds. The steering wheel also shakes a little when it hits a bump. Tires are brand new and it also did it before the new tires were installed. Also it will start what sounds like feedback hum through the radio and stops as you come to a stop. It kinda like the old school cars that had points for those of you old enough to remember those days. Turning the radio up, down, or off does nothing. Thanks for your help in advance
 

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2005 CTS-V
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The service manual devotes over 50 pages to vibration diagnosis and the list of possible causes is extensive. In addition to the normal causes, the T-56 Tremec suffers from a weak 6th gear that can result in highway speed vibration. The 6th gear problem is easy to identify because the vibration will disappear at the same highway speed in 4th or 5th gear. (see attached.) Were the new tires force balanced?
 

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Discussion Starter #3
The tires were installed at the dealership. I drove the car before on the test drive and it felt like a unbalanced tire. I bought the car and made a deal for new tires which were installed and the same vibration occurs. Not sure what balancing they did.
 

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2005 CTS-V
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Most highway speed vibration issues ultimately turn out to be tire or wheel related. Before pursuing the more unusual causes (other than the transmission 6th gear, which is easy to check), I would make sure none of the wheels were bent; check all of the rotors/hubs for runout; have all four tires force balanced; and have a 4-wheel alignment done.
 

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Discussion Starter #6
The vibration is there in all gears at highway speed so I feel like that will rule out 6th gear
 

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05 maggied CTS-V, 2017 NSX Whoo Hoo!
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Does the vibration go away when you push in the clutch?

If yes, then transmission/clutch/ probably dual mass POS flywheel.

If no, could be driveshaft coupler, driveshaft/ (bearing).

As for the vibration when over a bump, steering rack, struts/bearings/supports.

Stock motor mounts?
 

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Discussion Starter #8
No it it still there when I push in the clutch. I have tried in 4th 5th and 6th, clutch in and out, car at idle and reved. You mentioned driveline and that was a thought too. My 1 ton truck has a worn carrier and has a little vibration as well. I may just pull the driveline and have it completely rebuilt just to totally eliminate it. Im leaning towards bad struts on the front as well. Time to go after market I guess. Thanks for the help

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And yes I would assume stock motor mounts......car was bought new and traded back on new car trade before I got it. It is completely unmolested until now
 
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