2021 6.6 gas Hollow tapping noise

Dusilligaf · March 23

My 2021 2500 HD Denali has 119k on it. I warm up the truck every morning for 5-8 minutes, drive it down the street all good and normal. Soon as I get it under load about 1800-2000 rpm up the hill it gets a hollow tapping noise from the driver side of the motor only while accelerating, its increase and decrease with RPM's. Does this for the next few accelerations for about a mile then goes away completely. If I shut the truck off and its sits 20 minutes 1/2 hour it will do it again for a mile or so and go away again. Once it goes away I can drive it all day and it doesn't make the noise anymore.

Is it a lifter?

I have done 2 oil changes since it started doing this, nothing has changed. My extended warranty just ran out and I don't know what direction to go in with this

PunchT37 · March 23

Without a vid, it could be a lifter, or a LSPI case. Try 93 octane and see if the condition changes.

Dusilligaf · March 23

does not sound like a pre ignition knock, I tried adding a video but the file is too big. i\I'll have to try and get another

Jettech1 · March 24

On 3/23/2026 at 4:14 PM, Dusilligaf said:

My 2021 2500 HD Denali has 119k on it. I warm up the truck every morning for 5-8 minutes, drive it down the street all good and normal. Soon as I get it under load about 1800-2000 rpm up the hill it gets a hollow tapping noise from the driver side of the motor only while accelerating, its increase and decrease with RPM's. Does this for the next few accelerations for about a mile then goes away completely. If I shut the truck off and its sits 20 minutes 1/2 hour it will do it again for a mile or so and go away again. Once it goes away I can drive it all day and it doesn't make the noise anymore.

Is it a lifter?

I have done 2 oil changes since it started doing this, nothing has changed. My extended warranty just ran out and I don't know what direction to go in with this

After reading your post several times, (I'm getting older now LOL so try and cut me some slack) Anyhow my guess is you have have an exhaust leak. They tend to "heal" themselves with heat due to heat expansion. And you perfectly described an exhaust leak, probably just a small one. Perhaps the header gasket. They sound hollow and will go away with heat. I hope this helps sir. And if I'm not mistaken here, there was a problem with the early 2020's plus here with header gaskets. Please someone else chime in here if I'm wrong, but I do believe there was a problem with some owners.

Edited March 24 by Jettech1

Dusilligaf · March 26

I though it was an exhaust leak at first, i spoke to a GM tech and he said the same and to check the manifold bolts and flanges. But after thoroughly examining the bolts, they're all there and none broken, and i cant find any evidence of soot or blackening anywhere to show where it would be leaking from

Another JR · March 26

After the noise starts, do you hear it when the engine is at idle or only when pressing the gas pedal? If you don’t hear it at idle I suspect it’s not a stuck lifter.

Dusilligaf · March 27

I do not hear at idle at all, not even driving down the street, until its under load at about 1800-2000 rpm. If i let off the gas it goes away until i hit the gas again. After about a mile the noise is completely gone for the rest of my drive

Another JR · March 27

1 hour ago, Dusilligaf said:

I do not hear at idle at all, not even driving down the street, until its under load at about 1800-2000 rpm. If i let off the gas it goes away until i hit the gas again. After about a mile the noise is completely gone for the rest of my drive

Based on this I would suspect an exhaust leak before a stuck lifter.

MORSNO · March 27

Exhaust leak is the most probable cause of the noise, but I'd also look at the fan clutch and/or the fan shroud for an obstruction.

GMCustomerService · April 2

Our team sees you're having engine noise challenges with your Sierra and would like to offer our support to you so we can assist best. To get started, kindly send us an email with these details to [email protected]. With that, please ensure you include "Dusilligaf/GM Trucks Forums" in the subject line of your email. We certainly look forward to assisting you further.

AT4X Steve · April 21

I have had this noise as well as have others. From what GM and the local dealer told me, this noise is normal and likely the HP fuel pump for direct injection.