GMC Envoy Mystery


#1

I have a 2004 GMC Envoy SLT that is about to turn 10 in October. I have had a lot of maintenance done on this vehicle recently so that I can get a few more years out of it. There is one last issue I would like to get repaired but I have had it to 4 different mechanics and no one can figure out what is causing the issue or what if any issue it may cause in the near future.

The vehicle runs great when I am driving it, however, when I stop at a light and am sitting idle, there is a pretty significant vibration underneath the front end which causes the dash and rest of the front end to vibrate, and it is pretty loud. If while sitting at the light, I put the car in neutral or park, it completely stops vibrating and making noise and idles like it normally should. I have discovered that this happens when the vehicle is in any forward gear but does not happen in reverse as well as neutral and park. I had two mechanics say it was the clutches inside the transmission so I went straight to a transmission shop. One of the mechanics hopped right in my car and we went for a drive, at the same time he was connecting a device under the steering column (I assume some kind of diagnostics reader) and he immediately said the issue is definitely not the transmission. So I took my vehicle to the 4th mechanic and they could find absolutely nothing that would cause this issue and had no answer for me at all after having my vehicle in their shop all day.

One thing the transmission guy tried was, while I was sitting in the car, with it in drive as I would at a stop light, he used a jack to raise the front of my vehicle, the noise was still happening. He then moved over to the passenger side of the vehicle and jacked up the front side of the car from that angle and what do you know, the noise completely stopped and the vehicle was idling normally as it should. He explained this to the next mechanic I took it too and they still could not figure it out.

Has anyone ever heard of this or have a clue as to what may be causing this? The car runs great otherwise, the noise and vibration is mostly just really annoying at this point but I feel like there has to be a solution!

Thank you for reading my post. Any suggestions or comments are appreciated.


#2

I believe you have a bad motor or transmission mount. Metal on metal will cause the vibration and noise that you are experiencing. I had a bad motor mount on my Silverado that even shook the steering wheel and it had to be in gear to do so. It’s very easy to diagnose so I really don’t see why any of your mechanics has found it yet. Have them check the engine harmonic balancer as well. It’s a long shot but they can cause all kinds of vibration if the bolt is loose.


#3

I had one of the transmission mounts replaced already because the mechanic insisted that would fix the problem… it did nothing. The last mechanic who looked at it said the motor mount are rubber and the reason the noise/vibration stopped when the vehicle was jacked up on the passenger side is because there was pressure on the motor mount and that was causing the vibration to stop. My first thought originally was motor mounts but everyone keeps insisting it is the transmission. It literally only happens in drive! I will mention the harmonic balancer to the next mechanic I take it to which will likely not be one of those I have already been to! I appreciate you taking the time to post a response! Thank you!