2016 Silverado 5.3L - Thump Sound When Starting Engine

[Mad Maxx]

So the other day I noticed when I started my truck after sitting for a few hours, it make a thump sound. It makes the sound during the transition from when the engine is cranking to when it actually starts running.

 

It almost sounds like someone hits the floor or firewall with their fist. It's a solid thumping sound...or kind of like something was "stuck" but breaks free or loose when the engine starts.

 

There's no difference in drivability, no CEL's, nothing out of the norm. I just hit 2k miles.

 

The only thing I've noticed (and this has been going on LONG before the thumping sound) is it feels like the truck stutters when you lug it. Almost like a misfire or converter stutter. But I just chalked that up to the quirkiness of the TQ Management / 8-speed antics. I also get the random shaking when parked like described in the Motor Mount Shim fix threads. But again, that was all going on long before this thumping sound.

 

Anyone else experience this / have any ideas?

[Sierra Jon]

I have not experienced this but it sounds like it's pre-ignition/back-fire...

 

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[rickytickyshorth]

Loose plug wire?

 

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[Mad Maxx]

Loose plug wire?

 

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Checked em, but I'll totally take them off and reinstall.

[Dnt]

So the other day I noticed when I started my truck after sitting for a few hours, it make a thump sound. It makes the sound during the transition from when the engine is cranking to when it actually starts running.

 

It almost sounds like someone hits the floor or firewall with their fist. It's a solid thumping sound...or kind of like something was "stuck" but breaks free or loose when the engine starts.

 

There's no difference in drivability, no CEL's, nothing out of the norm. I just hit 2k miles.

 

The only thing I've noticed (and this has been going on LONG before the thumping sound) is it feels like the truck stutters when you lug it. Almost like a misfire or converter stutter. But I just chalked that up to the quirkiness of the TQ Management / 8-speed antics. I also get the random shaking when parked like described in the Motor Mount Shim fix threads. But again, that was all going on long before this thumping sound.

 

Anyone else experience this / have any ideas?

Any Mods to the truck CAI - Exhaust - Tuning - Lift kit etc?

[HondaHawkGT]

Could there be an exhaust leak? There are a lot of exhaust connections under the driver/passenger seat. A leak at one of the cats might be letting some gasses by before it heats up and seals better.

 

My truck has a pretty mean bark when it first lights off in the morning.

[Donstar]

I would take it to the dealership and have it repaired. What you are describing is not normal behavior and you should not be attempting diagnosis and repair in my opinion. With a new vehicle under full warranty I have the dealership do all of the repairs even if I know how!

[Mad Maxx]

Any Mods to the truck CAI - Exhaust - Tuning - Lift kit etc?

 

Everything that is done to the truck has been long loooong before this noise started.

[Mad Maxx]

I would take it to the dealership and have it repaired. What you are describing is not normal behavior and you should not be attempting diagnosis and repair in my opinion. With a new vehicle under full warranty I have the dealership do all of the repairs even if I know how!

 

My Dealer is clueless when it comes to anything other than oil changes, and I DO NOT trust them to even do that.

[dcheeseman]

Check the motor and transmission mounts, the engine/tranny shake slightly when starting, a loose mount can make them shake even more and possibly hit something while starting.

 

Daniel

[Donstar]

 

My Dealer is clueless when it comes to anything other than oil changes, and I DO NOT trust them to even do that.

If I didn't trust my dealership's service department then I would go to another authorized dealer and/or contact a GM Customer Assistance representative (1 800 462 8782). You paid to have your truck function properly for at least as long as its warranty period. Fixing it yourself could jeopardize having a future related warranty repair.

[AllTerrainX]

So the other day I noticed when I started my truck after sitting for a few hours, it make a thump sound. It makes the sound during the transition from when the engine is cranking to when it actually starts running.

 

Anyone else experience this / have any ideas?

Can you post a video?

[seansharley]

+1 on the motor mounts, I would lay under the truck and remote start it to look for something coming in contact. Maybe an exhaust pipe hitting something while the truck starts. I know mine jumps whenever I start it

[GMCustomerService]

Hello Mad Maxx,

 

I’m sorry to hear about this thumping sound when starting up your engine. I recognize how frustrating this can be, especially so early into your vehicle ownership. If you would like additional assistance, please feel free to send me a private message with your VIN, full contact information, current mileage and preferred dealership.

 

Regards,

 

Anthony J.

GM Customer Care

 

 

So the other day I noticed when I started my truck after sitting for a few hours, it make a thump sound. It makes the sound during the transition from when the engine is cranking to when it actually starts running.

 

It almost sounds like someone hits the floor or firewall with their fist. It's a solid thumping sound...or kind of like something was "stuck" but breaks free or loose when the engine starts.

 

There's no difference in drivability, no CEL's, nothing out of the norm. I just hit 2k miles.

 

The only thing I've noticed (and this has been going on LONG before the thumping sound) is it feels like the truck stutters when you lug it. Almost like a misfire or converter stutter. But I just chalked that up to the quirkiness of the TQ Management / 8-speed antics. I also get the random shaking when parked like described in the Motor Mount Shim fix threads. But again, that was all going on long before this thumping sound.

 

Anyone else experience this / have any ideas?

 

 

 

So the other day I noticed when I started my truck after sitting for a few hours, it make a thump sound. It makes the sound during the transition from when the engine is cranking to when it actually starts running.

 

It almost sounds like someone hits the floor or firewall with their fist. It's a solid thumping sound...or kind of like something was "stuck" but breaks free or loose when the engine starts.

 

There's no difference in drivability, no CEL's, nothing out of the norm. I just hit 2k miles.

 

The only thing I've noticed (and this has been going on LONG before the thumping sound) is it feels like the truck stutters when you lug it. Almost like a misfire or converter stutter. But I just chalked that up to the quirkiness of the TQ Management / 8-speed antics. I also get the random shaking when parked like described in the Motor Mount Shim fix threads. But again, that was all going on long before this thumping sound.

 

Anyone else experience this / have any ideas?