Dash or firewall rattle 6.6L gasser at stoplights

[UWSkier]

This only happens in forward gear with everything at operating temp.  If I sit with my foot on the brake, I get this rattle.  It goes away as soon as RPMs change even slightly so it doesn't do it in Park (which is why I can't diagnose it myself).  Anyone else hearing this?

 

2024 with the 10 speed.

 

https://photos.app.goo.gl/edm33P9k5v4Fu1E4A

[BuckWallace]

I was going to say there's a slight rattling noise when I have the HVAC on when I come to a stop (comes from the passenger side), but listening to your video that sounds nothing like it. I'd definitely get that checked out! Hopefully just something a little loose vibrating a bit.

[Flatus]

I have read a couple of posts on here where people have mentioned having a rattle caused by a loose bolt on the coolant reservoir.

[UWSkier]

On 12/31/2024 at 2:27 PM, Flatus said:

I have read a couple of posts on here where people have mentioned having a rattle caused by a loose bolt on the coolant reservoir.

thread necro time.

 

This was it!  One GM couldn't spare a $0.001 locking washer on the left-most coolant bottle bolt and it'd worked itself loose.

[No F-bdy Bs]

Mine has a slight rattle in the top, left corner of the driver's door window seal. 

[UWSkier]

5 hours ago, No F-bdy Bs said:

Mine has a slight rattle in the top, left corner of the driver's door window seal. 

That one drives me nuts.  Haven't been able to figure out how to fix that one.

[Epsilon Plus]

23 hours ago, UWSkier said:

thread necro time.

 

This was it!  One GM couldn't spare a $0.001 locking washer on the left-most coolant bottle bolt and it'd worked itself loose.

 

The worst part is its been a well known thing since at least 2022. 

[No F-bdy Bs]

On 6/17/2025 at 11:09 PM, UWSkier said:

That one drives me nuts.  Haven't been able to figure out how to fix that one.

If I press on it, it stops for a few minutes. Pisses me off because I KNOW I'd be wasting time telling the service writer. No chance in hell a tech could duplicate it. 

[EXSlider400]

Brand new 2500 gasser and when I drove it home from the dealer it was raining so did not notice it but mine rattles and I noticed the noise occurs when any pressure is applied to the steering wheel when at idle or any increase in any RPM. Could it be the hydraulic power steering? Sounds like a faint diesel clatter. 

[AT4X Steve]

I have the same rattle...goes away around 1000 rpm.   I looked at my coolant tank and my only question is does the rubber bushing simply ride on the bolt (it is not snug) or should there be a nut there.   If I jiggle the tank you can hear the bushing slapping.  BTW this bushing is on the firewall.

Edited June 23, 2025 by AT4X Steve

[EXSlider400]

On 6/23/2025 at 9:37 AM, AT4X Steve said:

I have the same rattle...goes away around 1000 rpm.   I looked at my coolant tank and my only question is does the rubber bushing simply ride on the bolt (it is not snug) or should there be a nut there.   If I jiggle the tank you can hear the bushing slapping.  BTW this bushing is on the firewall.

I don’t think it’s supposed to have a nut. Mine does not have one there either. I’m thinking the noise is heat is just power steering pump and fluid flow…. only because my last vehicle was a 1500 with electric steering. 

[AT4X Steve]

Thanks!

 

[UWSkier]

On 6/23/2025 at 7:37 AM, AT4X Steve said:

I have the same rattle...goes away around 1000 rpm.   I looked at my coolant tank and my only question is does the rubber bushing simply ride on the bolt (it is not snug) or should there be a nut there.   If I jiggle the tank you can hear the bushing slapping.  BTW this bushing is on the firewall.

That's how mine looks.  My bolt on the bottle that threads in to the fender sheet metal from above was loose.  I pulled the bottle up tight to the side of the frame there, tightened that 10mm bolt down to reduce the load on that bolt with the bushing, and noise is gone.

[AT4X Steve]

14 hours ago, UWSkier said:

That's how mine looks.  My bolt on the bottle that threads in to the fender sheet metal from above was loose.  I pulled the bottle up tight to the side of the frame there, tightened that 10mm bolt down to reduce the load on that bolt with the bushing, and noise is gone.

So the bolt in the rubber bushing is centered in the bushing now?

[UWSkier]

On 6/27/2025 at 8:00 AM, AT4X Steve said:

So the bolt in the rubber bushing is centered in the bushing now?

Actually, not really centered, just not making noise because the bottle can't move anymore.