FogDucker

As my Continentals become more worn, the buffeting has reared it's ugly head - again. This, in addition to a developing CLUNK that can be felt when shifting out of park, clicking/knocking sound in the steering wheel [fixed twice] and squeaks from the inside rear was the final straw. On Friday, I'm parting ways with the Yukon after ~125,000km over nearly 5 years. Ownership has been bitter-sweet. The 6.2L was definitely the highlight - what an awesome engine! The buffeting, prominent on so many K2XX trucks is regrettable. Thanks to all on this forum for the fact sharing and connections made. -- Marc

The booming definitely wasn't tire related for me - that was fixed on a separate trip. Welding the dampers on the exhaust 100% solved the booming that I heard when the rear wheels went over bumps [including snow] at low speeds. It sounded like somebody was flicking a large subwoofer. Somewhere in this thread, I included pictures and measurements on where they were placed. The buffeting issue was fixed by road-force balancing my stock 20" tires to be 10lbs or better as per GM specifications. They resolved it *after* the fixed the booming issue and it took them 6 tire replacements to make it happen! -- Marc

When in tow mode, the screen changes to add the transmission temperature and two little boxes as shown in the picture. Does anyone know what they are or what function they provide?

I don't, no. The vibrating could be felt in the seats and the steering wheel. The whole assembly was replaced - brake rotor to brake rotor. -- Marc

More clues that the roof is the root cause. My Yukon also had the headliner pulled down and re-glued, but it did nothing. Perhaps these panels prevent the thin metals roof from resonating?!? I recall somebody else in this thread made some shims that were placed between the cross bars to apply pressure to the roof, also preventing movement. I also remember that others spraying the underside of the roofs with spray foam, but didn't have positive results. My rear axle was replaced which solved my vibration problem, not the buffeting problem. booming noise -> fixed by adding weights/dampers to the exhaust buffeting -> work around by having well balanced tires vibrating -> fixed with rear axle replacement 80,000km after the repairs, the truck runs great and I plan on keeping it another couple of years. Only the buffeting rears it's ugly head every now and then, but I know what to do! ../mk

Hi EXSlider400, I'm not familiar with any exhaust flappers, but what you describe is the "buffeting" that is discussed in this thread. I have 70K miles on my Yukon now and can say with certainty that out-of-balance tires are the trigger. The root cause is actually something else such as a thin roof being triggered by out-of-balance tires, but the only thing you can control is the tires. Why am I so certain? Because my dealership had to replace 6 (!) Continental tires to get mine to run smooth and quiet. When I put my winter shoes on [BFG KO2s, road force balanced to 8lbs or better], I never had any buffeting. The Continentals will occasionally flat spot when cold, introducing buffeting. Warm them up and it goes away. I can still hear/feel the buffeting every few months, but only on the Continentals and only when cold. I had the dealership re-balance them 2 years after the initial fix and it improved. Have your dealership "road force balance" the tires to 10lbs or better. If they don't have a Hunter Road Force Balancer, find another dealership that does. GM has a TSB that states the requirement of 10lbs or better balance per tire on our trucks to minimize buffeting. It's buried somewhere in this thread if they're not already aware of it. I'll have to buy new summer tires in the spring and when I do, I'll be asking my dealership for 4 of Michelin's finest, road force balanced to 10lbs or better with the printout to back it up! I'll also budget an extra hundred bucks to have them road-force-balanced 2 years in, if required. -- Marc

I would have your existing tires Road Force Balanced to see what they're at. Not all shops have a proper RFB machine as they cost over 5 digits. The most popular brand is "Hunter". If you do order new tires, make it conditional that they RFB at 15lbs or better, GMs recommendation for the K2XX truck plaform. My BFG K02s balanced no worse than 8lbs. The best they could get out of the Continentals was 12lbs. Budget for RFB every year or two. This is the only known buffeting input that we can control. Sometimes turning the tires on the rim can get the numbers down. Other times you'll need to replace them. I've got 40,000 miles on my Yukon and my family of 5 enjoy it. Every now and then I'll get a brief whiff of buffeting if the tires flat spot, but it goes away. Buffeting = Out of Round Tires; peaks at 40mph and 70mph Booming = exhaust bouncing around when driving slowly over bumps

I didn't get the Borla, but my 'booming' over bumps was eliminated by clamping weights/dampers on the exhaust. I included pictures further back in this thread if anyone is interested in quantity and placement. The buffeting was a result of tires. It took 6 Continental replacements to get them quiet [under 10lbs] and I had them re-road force balanced when I putting them back on for the summer. The Continentals have a tendency to flat spot which temporarily re-introduces buffeting. I'm going to put up with them a little while longer and replace them with some Michelins for summer duty. My BFG KO2s are awesome and don't introduce any buffeting. That's probably why I left them on until August! If it wasn't for the fuel economy penalty [they are 14lbs heavier per tire!], I'd leave them on year round. The vibrating was fixed by replace the rear end. I've been enjoying my Yukon ever since and only experienced a failed wheel bearing since. While the root cause of the issue may never be fixed or identified on these models, I'm OK knowing that I can control the inputs [shitty or out of balance tires].

SierraMyst, My travels don't take me that far east in VA, so I parked my Yukon on a curb and crawled under this afternoon. I was mistaken - there are only 4 dampers. From front to back, they are: a pair of dampers close to the crossmember, before the braided section a single damper right after the braided section before the muffler/resonator a single damper approximately 11" before the other muffler/resonator Here are some more pics, in the same order as above. Hope it helps. -- Marc

Oh sure, ask the Canadian to crawl under his truck in January! ;) I will be rolling through the Virginias in a month or two on my way to Florida - got a lift? Next chance I get, I'll take a closer look and will snap some more pictures. -- Marc

I spent many hours trying to isolate the buffeting and booming and last winter, I even drove around snow covered roads with all windows open and then only with the hatch glass open - the low speed over-bumps booming was still there. This should rule out the "air tight cabin" theory. I also drove around for a while with Active Noise Cancellation disabled - it had no influence on the buffeting or booming. My roof rails were installed after my 3 issues (booming, buffeting and vibrating) were fixed and I never tried wedging anything on the roof to limit movement. I'm still not sold that it's the sheet metal, but this is outside of my area of expertise. There are some interesting companies that specialize in this sort of thing and could definitively identify the root cause at a cost. I would have expected the Suburban, with a longer roof, to exhibit a different buffeting sound than my shorty Yukon. The one that I drove for a week sounded exactly the same as mine at exactly the same speeds - 40mph and 70mph. Also, if it were sheet metal, I would have expected a higher percentage of vehicles (all?) to have this issue and that doesn't seem to be the case. I also would have expected to feel something inside the cabin at 40mph and 70mph if something was vibrating the roof. I crawled around the cabin and touched every part I could, including the metal floor boards, in every seating configuration while a neighbor drove around. I couldn't feel or hear anything as the buffeting occurred. One way or another, there is an unwanted transfer happening that excites something. Maybe it is the roof. Stiff body mounts certainly seems plausible, but I don't think anyone has explored it a great deal. I think Wrench had them loosened/tightened with some influence, but not replaced. I'd also be curious to learn if they changed body mounts between the last model and the 2015+ model. Brake rotor to brake rotor - the whole enchilada. It was shipped fully assembled in a wooden crate. -- Marc

I'm not sure if the 5.3L exhaust is the same or if it applies. If the "boom" sounds the same, I would suspect that it does. My Sierra AT wheels are OEM, also 20".

Correct. For me... Booming (yes, over snow, gravel and other bumps) was fixed with exhaust dampers. Buffeting was fixed by getting tires RF balanced to 12lbs or better. Vibrating was fixed by replacing the rear axle. I've put ~20,000 enjoyable kilometers on since all 3 were fixed. The buffeting started to creep back in fall and disappeared when I put my winter shoes on. I'm going to have the stock Continentals RF balanced (again) in the spring before I put them back on. If they're out of line, I'll get a set of Michelins or might just leave the Ko2's on all year as they've been great even though they're 15lbs heavier per tire than the Continentals.

5 dampers mounted with 4 u-bolts. -- Marc

If you look at the second picture that I linked to above (of my dampers), it looks like they put 2 dampers on one u-bolt. This was the only such one that I could see. The rest are 1:1.