RahinMVA

No, not at all from day 1; but it also wasn't anything sudden. It was a subtle ramp up over maybe the last 18 months or so to the point that I now notice the rough shift from 2 to 3 all the time; and the odd clunks described in my original post are now obvious. Just looked. No sign of oil. Also, FWIW, this truck has only been serviced at GM dealers.

Yes, I had the fluid & filter changed at about 48K, per the owners' manual recommendation. Symptoms were the same before and after the fluid change. It is hard to hear that this might be "normal." My only other experience is my old truck - a 2000 Silverado that had 185K miles on it when I bought it. Other than the typical clunk when shifting out of Park, it was very smooth.

Hi all, I have a 2015 GMC Sierra, 51K miles, and my transmission acts funny: - rough shift from 2 to 3 when starting from a dead stop - occasional "clunk" when decelerating from highway speed (foot off the accelerator) - when in stop-and-go traffic there is strange / clunky shifting between gears, occasional random "clunks", almost like it can't figure out what gear it wants to be in Any thoughts on these issues? Could it be related to the AFM / DoD? Could my transmission be going bad already with just 51K miles? Thoughts on how to correct this? Any input would be appreciated. Thanks! Rich

Just in case anyone visits this (very old) thread, here is what happened: Eventually, the dealer was able to hear the rattle. They replaced most of the exhaust system, and now it is perfect!

I hear you. The trouble is that the sound is intermittent. I can't duplicated it on demand. Over the past two days of driving, I haven't heard the noise at all. What I don't want to do is waste my time with multiple trips to the dealer trying to duplicate the noise. If I could try to narrow it down and maybe discover the source myself, then it is just one trip to the dealer to fix a known problem, instead of many trips trying to guess what the problem is. BTW - I have just over 600 miles on it now.

Thanks for the suggestion. I'm not 100% sure, but I don't think that the converter on this truck has a shield of the type that is attached directly to the converter. On my truck, there is a long shield attached directly to the underside of the truck, above the converter, and it is fixed securely. I try to make it rattle by tapping on it and it stays secure. There is no shield that wraps around the converter or is attached to any of the exhaust system itself. Unless I'm looking at the wrong things, it isn't the converter shield making the noise I'm hearing. I suppose it could be one of the bolted-on shields up higher on the exhaust system - like right near the manifold. But I've also tried to tap on that to make it rattle and I have been unsuccessful at making the noise.

I have a new 2015 Sierra 1500, and I first heard this rattle on my way home from the dealer ( a 3 hour drive ) when decelerating from highway speed at an off-ramp. The truck had 58 miles on it when I bought it from the dealer's lot. 5.3L V8 engine, 4x4, Z71 It is an intermittent mechanical rattle - appears to be originating in the engine compartment, probably passenger side - more noticeable at low speeds, but does not seem to change directly with either ground speed or engine RPM - varies in intensity, volume, pitch and rhythm, but I can't tell what makes it change. - seems to be loudest / most intense when stopping or starting at low speed - like at a stop light or in the drive through - when I am on and off the accelerator very lightly. Two key examples: First, I was stopped at a stop light and just took my foot off the break and it got loud. Each time I put my foot back on the break, it stopped momentarily. Then, at the next light, my foot was on the break and it was loud. When I took my off the break and put it on the accelerator, the sound stopped. Second, I was going through the drive through and with my foot on the break at the order menu, no sound. Then I slowly pulled around to the window and as I went very lightly on the accelerator, the sound got very intense momentarily, and then varied in intensity and volume the entire time I was sitting still with my foot on the break. Occasionally I'll drive for 50 miles or more and not hear it; but most of the time it is almost constant. It never happens when the truck is in park and idling in my garage. It always seems to stop right before I try to stop, pop the hood, and listen for it. Any ideas on what I should look for? Thanks!