Technical Car Experts Answers everything you need: Vibration noticed while driving towards floor board near transmission?

In this case the driver noticed vibration at high speed.
The vibration noticed towards Transmission and firewall.
Vibration is noticed at 1200 to 1500 Rpms.The vibration goes away,when gas pedal is released.

This problem is noticed on 2009 GMC Yukon.

There are a few things we can do to narrow down which area of the vehicle that may be causing the noise. Most of these things will require an area where you can drive the vehicle in a safe place, preferably a large empty parking lot. Do you have a space where you can drive it and do some testing? Does the noise only happen above a certian mph? I know you said it was engine speed related, is the noise present at low speeds when the engine is at 1200-2000 rpm? Is your Yukon 2wd or 4wd? By all means if you do not feel safe driving the vehicle then have the dealer tow it back to the shop so they can fix it for you.

Ok, so it sounds like the vehicle is stock and has not been altered. Sometimes after-market, and even GM approved accessories, can cause concerns similar to yours. The DIC display sometimes will show you what mode the engine is in, usually this display is coupled with the fuel economy info. You should be able to find this by pressing the fuel and vehicle buttons that scroll through the trip odometer and such. You can set it to any of the displays to watch while driving. Is the vibration you feel only occurs in the 4cyl mode. I have run into very similar concerns with owners of the new 2010 Camaro. The vibration and exhaust note change noticeably when the vehicle switches into 4cyl mode. After driving several of these cars and speaking with GM engineering, it was concluded that this was a normal operating carachteristic. So if your Yukon only experiences this in 4cyl mode, this may be a normal condition. You could double check this by taking a test drive in another Yukon with Active Fuel Management. If the comparison vehicle also exhibits this condition it is likely a normal characteristic. I also did a bulletin search for your vehicle and did fond one bulletin that may apply. You have very low miles, and it started on day 2 so it's an outside chance but still worth having the dealer check. I will post the bulletin below for you. If the vibration is noted try accelerating to get the engine to switch back into 8cyl mode to see if vibration diminishes.

Subject:

Vibration Felt and Heard During Low RPM Driving - Inspect for Trans Mount Debris

Models:

2004-2007 Buick Rainier

2001-2009 Cadillac Escalade

2002-2009 Chevrolet Trailblazer and Trailblazer EXT

1999-2009 Chevrolet Avalanche, Silverado, Suburban, Tahoe

1999-2009 GMC Sierra, Yukon

2002-2009 GMC Envoy, Envoy XUV and Envoy XL

2003-2009 Hummer H2

2002-2004 Oldsmobile Bravada

2005-2008 Saab 97x

This PI was superseded to include Full Size Trucks and Utilities. Please discard PIT3516C.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:

An unusual vibration may be felt and heard at very low RPM, especially during parking lot maneuvers or driving at lower speeds and making a gradual left or right turn. A rattle may also be heard from under the vehicle that can be felt in the floor as the engine is started due to Powertrain movement. If equipped, this may be more pronounced when AFM (Active Fuel Management) is active.

This may be due to stones and debris being trapped in the transmission mount as shown below, which may transmit the noise/vibration into the body.

Example of a 2008 Silverado Shown Here

Recommendation/Instructions:

If SI diagnosis does not isolate the cause of this concern, remove the transmission mount and clean the debris out of the mount. Then install a 5.5" (14cm) section of 0.75" (19mm) heater hose into the cavity of the transmission mount to prevent debris from entering the mount as shown below, reinstall the mount, and re-evaluate the concern.

Notice: There should be no need to replace the mount when this issue is encountered.

Example of a 2008 Silverado Shown Here.