High-speed vibration

[nfisherman]

Hello, I'm hoping someone can help me find a vibration in my 2008 Yukon XL SLT, 1500 4x4, 5.3L, 120,000 miles. I'm having trouble finding a vibration at highway speeds. Above 70 mph, I get a loud, low hum that stays the same regardless of speed, above 70, or whether my foot is on the accelerator or not. As soon as I drop down below 70 mph, the hum stops and everything is fine. I started noticing this after I took it to my dealer for a check engine light. The dealer replaced the purge valve above the spare tire. While it was there, I also had all of the lubricants and belts replaced. I mentioned that I'm going on a road trip soon. The dealer said he'd do a comprehensive inspection. He didn't mention any problems after the inspection.

 

I've also had the tires rotated and balanced and I replaced the rear brake pads and rotors. It needed brakes anyway. None of that changed anything. The hum sounds like it's in the rear of the vehicle. I had my son sit on the floor in the back while I was driving and he said he could feel the vibration. I can't feel anything in the front. I feel nothing at the steering wheel.

 

I can take it back to the dealer and ask about it since it seems to have started after the last service. If it's something easy, though, I'd prefer to just fix it and save another trip, loaner car, etc.

 

I'd appreciate any ideas.

 

Thanks.

 

 

 

 

 

 

[thearborbarber]

If it were my rig, I would pull the driveshaft and check the u-joints.

[scooby5121]

If it were my rig, I would pull the driveshaft and check the u-joints.

Replace the u-joints , and double check the rear end fluid level.

[Silverado4x4]

_{Also have them check the rear driveshaft balance.}

[nfisherman]

This is just weird. I thought something happened at the dealer during my last visit that may have caused the vibration. That wasn't it. A day or so after the service, I removed the rear seat so that I could shampoo some deer blood out of the carpet :-D. I didn't mention anything about the seat because I didn't think it would matter. It did! I put the seat back and went for a drive today. The vibration is completely gone. I took it up to 80 mph and everything was completely quiet. I guess I was getting some kind of harmonic vibration in the floor without the seat. Perhaps something is beginning to fail and the vibration is just too small to notice with the seat in. Either way, it's too small to worry about for now. I'm guessing I could spend a lot of money trying to find the problem. I'll wait until something really breaks.

 

Thanks for the suggestions.

[Wolfmanjohn]

Really? Make sure the spare tire is aired up to spec and winched up tightly against the frame.

[nfisherman]

The spare tire was the first thing I checked. I knew the dealer replaced the purge valve so I knew he had to move the spare tire to do that. The spare is solid. I also thought maybe it was the heat shield that keeps exhaust heat off of the spare. That's solid, too.

[SouthCo]

That's weird. I've never heard of noise caused by the rear seat being removed in the Yukon XL/Suburban of any generation. I know it's a different generation but we pull the rear row out of my wife's 2005 Yukon XL whenever we go on vacation and I've never heard a difference. I still wonder what's making noise that you can't hear with the seat in. Keep us posted if you ever find the culprit. I'd probably do the same as you and not worry about it for now since you can't hear it with the rear row in.