Firewall Noise When Cold And In Reverse

[Klink]

2008 Suburban and burning a ton of oil, GM decided to replace a bunch of the internals as I wait for "The fix" to come out.

 

Ever since the truck came back I get a vibrating noise when the truck is cold and I back out of the garage. It is somewhere the firewall that I hear it. Dealer couldn't duplicate it but I hear it almost every morning it is cold. Once the truck runs for about 20 seconds it is gone. It only happens in reverse and it appears to be tied to rpm's. If I tap the gas it is gone. If I just drop it in reverse it sounds like something vibrating against the firewall. Does not do it in drive, only reverse. The truck doesn't have to be moving either. I can hold my foot on the brake in reverse and it will do it for about 20 seconds or so.

 

Any thoughts?

 

They did replace the transmission lines when they did this work because they were leaking.

 

Thanks in advance for any thoughts!

[C. Charles Hahn]

Take it back to the dealer, and tell them to keep the truck until they can find and fix the problem. If they leave it sitting overnight and have a tech try it first thing in the morning exactly like you describe, they should be able to duplicate it.

[zedbear]

Perhaps exhaust related?? Maybe there is an issue with the exhaust manifold(s) to down pipe(s) connection(s). Happens sometimes after pulling all that apart. I had this happen with an car I had pulled the motor out of for repair. Except it was the other way around. When cold and in drive, it would tick. Putting it in reverse would make the tick go away because the motor tilts a bit in the other direction, sealing the leak at the collector.

[jblakeney]

Donuts any one?????? Probably exhaust..... When it gets hot you probably can here a ticking noise idling out side tooo.

 

Jbo

[Klink]

Dealer can't duplicate issue. I hear it every morning when it gets cold at night. I do not hear ticking when warm. I guess I will have to poke around the exhaust manifold and see if anything is leaking around there.

 

It is a weird vibrating sound. If you could imagine a hose vibrating against the firewall, that is what it sounds like to me. Problem is everything is tightened down.

[papastoy]

Maybe check under the dash to see if its something like an electrical harness vibrating against the firewall from the inside?

[Badass69]

Yeah my dumbazz dealer can't duplicate the shift flare from 2nd to 3rd in my 6L90E even though it does after everytime you start the truck and also when dead cold. Had it for 3 days and no of course not....

 

Take the truck in, leave it sit there overnight. If you can, go in and do a ride along with the monkey that is going to work on it. That will guarantee he hears it...... and then you find out he's deaf, lol.

[DaleJrRocks88]

take it back and tell them to look at the vacuum hoses routed to the intake, there used to be a bulletin about removing a plastic retainer on the firewall.

Yeah my dumbazz dealer can't duplicate the shift flare from 2nd to 3rd in my 6L90E even though it does after everytime you start the truck and also when dead cold. Had it for 3 days and no of course not....

 

Take the truck in, leave it sit there overnight. If you can, go in and do a ride along with the monkey that is going to work on it. That will guarantee he hears it...... and then you find out he's deaf, lol.