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Update now that I've had the truck back for a week: I dropped my truck off Monday 8/4 to have them look into the terrible clunking noise in the rear and they called back stating the leaf spring was definitely bad and that they were going to replace it when the new springs came in the morning of 8/5. I picked my truck up at noon on 8/5 and the rear has thankfully made no noises since then. Fun fact: either if fell off or they forgot to install one of the rubber pads in the rear leaf so I had to make trip back to get that installed once they found it off the old spring that they removed. I do however have a new creaking noise coming from the driver's side front wheel. I can recreate the noise just by rocking the truck side to side but I have the ProComp 2.25" level kit on the front so I'm kind of weary about bringing the issue up to the dealer and them telling me I'm out of luck due to the added leveling kit. Any advice? I'm starting to get discouraged at the issues I've already experienced in the 24,000 miles I've had the truck of what's to come. I started playing around and discovered that based off the KBB value(I didn't research NADA, Edmunds, etc.) my truck is still worth just a little more than what I paid for it, so I am contemplating selling it outright and buying a new '17...

Update for everyone after having the truck back for a week: There was a significant decrease in the idle and engine ticking after the dealer replaced the vacuum pump, however, I still notice the faint "exhaust leak" that has been present since ~2,500 miles on the truck. I paid extra attention to the loaner I drove during the two days mine was in the shop and never heard a noise similar to what mine makes. The dealer stated they checked all around the manifold for any sign of leak and did not notice anything while test driving, but I can say that the loud vacuum pump far overshadowed the exhaust leak. The vacuum pump replacement indeed fixed the rough sound at idle, but I still believe there is a minor exhaust leak that the dealer didn't notice. I think my next step is going to make an appointment at the Chevy dealer down the block from my office to see what they can do. Side note; my rear passenger side leaf spring went bad(made a terribly embarrassingly loud noise while driving) so they replaced both leafs in the rear, and I now have a creaking noise coming from the driver's side front wheel. I can recreate the noise just by rocking the truck side to side but I have the ProComp 2.25" level kit on the front so I'm kind of weary about bringing the issue up to the dealer and them telling me I'm out of luck due to the added leveling kit, any advice?

I dropped my truck off yesterday for the clunking issue I've been describing. They said the leaf spring was bad so they're getting that replaced today once it shows up. I asked them to re-torque everything as well since the loaner I have road like a dream compared to my truck. I'm hoping this will resolve my suspension clunking issue but we'll see when I get it back. I'll make sure to update everyone in a few days with results!

I dropped my truck off at the dealer yesterday and told them to take it for a drive and inspect the driver's side exhaust manifold, without mentioning anything else(lifters, fuel pump, vacuum pump.) I received a call a few hours later stating my vacuum pump was bad so they replaced that. They are also replacing a bad leaf spring in the rear today so when I pick up my truck I'll update you all on the conclusion. I'm hoping this is the fix but it's hard to be optimistic when my truck has 23,xxx miles and a bad vacuum pump and leaf spring...

UPDATE: I had an appointment at the dealership yesterday to diagnose this along with another issue and unfortunately, the dealer wasn't much help. The tech. that I spoke with was insistent on the "exhaust leak" being the vacuum pump making the noise, so it sounds like that's going to get replaced first. The vacuum pump does make a terrible ticking noise at idle but there is definitely an exhaust leak while driving but it is shadowed by the vacuum pump at idle. I guess I can understand where they're coming from with not wanting to immediately tear apart the manifold but it's frustrating that I'm going to have go through some headaches to get all of this resolved. My biggest upset was a recent clunking issue in the rear which has been more and more present lately. It's obviously a suspension issue in the rear and I could replicate the noise all day to the dealer who kept saying it's "play in the axle" which it most certainly is not. The appointment was only supposed to be diagnostic and they didn't seem to find anything to fix with the few issues my truck has so I'm scheduling an appointment to drop it off in a week with a list of everything that needs fixed. If I can't get my brand new truck to perform the way it should then my next step will be filing a complaint with the BBB, which will hopefully get GM moving more seriously towards resolution.

Unfortunately, the dealer wasn't much help yesterday. The tech. that I spoke with was insistent on the clunking issue is actually normal "play in the axle." It's obviously a suspension issue in the rear and I could replicate the noise all day by bouncing on the truck and we even went for a test drive, but they seem to think it's a non issue. The appointment was only supposed to be diagnostic and they didn't seem to find anything to fix with the few issues my truck has so I'm scheduling an appointment to drop it off in a week with a list of everything that they need to fix. If I can't get my brand new truck to perform the way it should then my next step will be filing a complaint with the BBB, which will hopefully get GM moving towards resolution.

I'm experiencing the same "clunk" as of about a month ago. I initially thought it was due to the trailer hitch and log chain that I keep in a bag in the bed of the truck but the noise started to annoy me so I took everything out of the bed and the clunking is still there. I can replicate the noise by shaking the whole truck side to side by pushing on the bed rails or when I'm driving in revers and suddenly stop. I have an appointment at the dealer today to have a tech diagnose another unrelated issue and plan on bringing the clunking issue up as well. Will keep everyone posted!

@GM Customer Service please send me a PM, your inbox appears to be full

I don't notice the noise in mine during a normal idle, and typically not when I rev it up in park. The noise comes from the driver's side floorboard and sounds very similar to an exhaust leak mostly in lower RPM's while moving, both in V4 and V8 as well with A/C on and off. The noise is not present 100% of the time, but it is present both in town and on the highway as well towing/not towing. I have another oil change due in ~2k miles, and I would typically perform these myself as I already used the two freebies from the dealer, but I would be open to dropping my truck off at the dealer if a resolution is found and letting them perform my next oil change while they're under the hood

I've been a longtime lurker on this thread and just now posting as I have had this similar issue since about 4k miles in my '16 GMC Sierra SLT 5.3L that I bought in June '16. Had the dealer look into a "possible exhaust leak on the driver's side" when I brought it in for the first oil change at around 6k miles and they claimed it as a normal fuel pump noise. My truck is at ~22k miles now and the issue has not gotten any better or worse since I first noticed it. Following this thread to hopefully find a permanent solution!