Tapping Noise On Acceleration

kwoodwo · September 27, 2014

Anyone have a fix for this? Same thing happening to me as in the video on a 6.2 denali.

michigan2500hd · October 1, 2014

My 6.2 taps really bad on a cold start in the morning. I have to let it warm up a few mins before driving and it goes away. Really bothers me as to what the heck it could be. It's like this all year not just cold weather.

Edited October 1, 2014 by michigan2500hd

servantsalesmen · October 2, 2014

Flexplate. That's what I'm calling. Start your truck up and then get out of it and crawl underneath it and try to find the source of the sound. If it seems to come right from the bell housing on the tranny, you probably have a bad flexplate. Mine cracked in like 8 places and sounded terrible.

michigan2500hd · October 2, 2014

Would the noise go away once the engine is warmed up? I notice mine has what I thought was a little valve train noise when idling in park but I could just be "over listening" to it. Do the 2011 silverados with the 6.2 have a history of bad flex plates?

servantsalesmen · October 2, 2014

GM uses a crappy stamped steel plate for their flexplates and they can break. It's not super common but also not super rare. Typically a cracked plate is loudest when the engine is running unloaded meaning in park or neutral. When you shift into gear or start to accelerate you put a load on the plate and that force is enough to push it together enough to keep it quiet but the minute you coast and let rpm drop the noise comes back. If it is a flexplate, fix it! Don't let it go. Yes it is possible to put several thousand miles on a broken one but it's a disaster waiting to happen. If it totally let's go and grenades itself, there is a big metal disc heading right into the cab and it will slice through the truck like butter.

Edited October 2, 2014 by servantsalesmen

kwoodwo · October 3, 2014

It is not the flex plate. You are describing something entirely different. When the truck is in neutral or park, there is not tapping. You can rev the engine in park or neutral and there is no tapping. However, once it is in gear there is tapping at low rpms around 20mph-30mph when you lightly "feather" the gas pedal.

The GMC dealer told me that it has something to do with my front differential but I am hesitant to let those guys have their way with my truck without knowing for sure what it is.

kwoodwo · October 3, 2014

Update: spent $1200 getting new front differential bearings installed. Problem is still there.

servantsalesmen · October 4, 2014

That's frustrating man. Sorry to hear that. Best of luck with this one. Please let us know if you find it

KWIKNVA · November 6, 2014

My 09 Denali is making the same knock. Sounds like the growl from the predator when driven cold. I can shift into neutral at speed or parked at idle and rev the engine with no knock. Once the tranny hits 120 degrees and the motor is at 205-210 the knock goes away. I've heard piston slap and lifter tick before, slap and tick generally go away in 30-60secs unless extreme cold temps. My knock is there are long as the trans and motor are under 120/210. Is this a tranny issue? pump or converter???

Best way to describe the knock when accelerating is this.

http://youtu.be/OQwA14YWdqA

Has anyone had this fixed?

GMCustomerService · November 6, 2014

Hi KWIKNVA,

We're sorry to hear that you are also experiencing this clicking noise in your vehicle. We can certainly understand how frustrating this must be. Unfortunately, we're unable to provide technical advice, but we'd like to look into this for you. Feel free to send us a private message in reference to this thread if further assistance is needed. We look forward to hearing from you!

Kristen A.

GM Customer Care

dbroman3 · November 7, 2014

Can anyone confirm that they have the same noise that is in Z06killers video ? also found at this link

It is exactly what I have. Almost sounds driveline related, possible axle or front drive shaft being that it is AWD. It does NOT make the sound during rev only under driving acceleration.

I do hate the sound but more interested in making sure it isnt something major that can go out on me while driving.

KWIKNVA · November 8, 2014

That "Rattle" noise in the video by Z06killers sounds to me like the rattle described as the flexplate rattle ( sounds like heat shield rattle) which is common. Hard to be certain as it also sounds like he is driving on a gravel road with the windows down. Clearly to me it isn't a "knock". I'm like kwoodwo. He has almost described my symptoms. My issue is what would cause a knock that actually goes away once the tranny hits 120-130 degrees and the engine is at 200-210?? However, the knock I hear is at 1000-1800 rpms. I can bring the truck to 30-40mph and shift into neutral and rev the motor and no knock at cold temps. I can idle on a cold start in park and no knock. Once in gear and I accelerate the knock is there until the temps come up which takes about 5-10mins. Not piston slap which would go away on avg. 5-60 secs after start up. I listen to a video with a 6.2L with piston slap and it sounded like someone banging a aluminum bat against the block. My knock sound just like the growl of the predator.

I've consulted two of my local tranny shops that have been in the business for 25 & 80 plus years and these symptoms didn't jump out at them as something they had seen before. The flexplate rattle is something they said they see often with the 6L80 trannys. So, I'm running out of ideas. Every logical idea seems viable until you throw the fact that the noise goes away when the motor isn't under a load or is at normal running temps. So, if it ain't Flexplate "rattle", "Piston slap", or "lifter tap" I have no SEL, no visible or audible exhaust leaks, no misfires or poor performance. Because the truck runs so good I don't see the need to pay crazy labor cost to have the motor or trans torn down. If I can pin point the the problem then I may throw cash at it.

kwoodwo! What was the end result?

Tbianch · November 9, 2014

I have a 2007 Yukon Denali with 187K miles and have the same noise as the you tube video. Usually occurs at 1800 rpm around 70-75 mph. I have taken to dealer for test drive so they could hear it twice and it did not create the sound. both times it was a rainy day. Anyone notice this either their issue? Reading these posts definitely seems like a systemic issue. hope somebody has figured it out.

gimleyd · January 14, 2015

Hi there I have the same problem but I know what it is. Its a cracked exhaust manifold or leak. Take off your heat shild have a friend plug the muffler and listen for any air or fum leaks. I got this info from a Chevy dealer and that's how I found the problem I am going to try to fix it tomorrow with a high temp liquid metal compound. I hope this was helpful and Ill post back with the results of the fix later.