2007 6400 miles completely stock and when the car has been driven and then parked once you start it back up it makes loud knocking sound what is that i searched through all the threads people occasionally talk about it but no one says what it is and how to fix it been to the dealer once going back again on monday second time in a week

 

does it sound like its coming from the bottom, like....tap,tap,tap,tap,tap

 

yeah its weird it doesnt do all the time just occasionally

 

does it do it when u turn the car off afterwards

 

nope only when it starts up you get in and start it up makes knocking sound 3 to 7 times and thats it

 

i had that sound, it was my exhaust expansion because of the onset of heat when u start the car, so the metal was expanding. but ive heard of ppl saing other things....but i assume thats what it would be

 

well how bout this if you turn the key to the on position but dont start it wait a few seconds then start it it never makes the sound and they was some times it has done it after the car has sat over nite but that was before it got really cold it doesn't make the sound as often cuase the battery is getting weak and it doesn't start as fast as it used to

 

ive heard some ppl say that chevy told them it was a bad axle, or some other ****...some ppl said chevy couldnt even tell them lol

 

yeah i had it at the dealership and they couldn't duplicate the noise i have talked to the plant that built my car they told me to take it back to another dealership the best was for the second time my car was a quart low and the guy says they do that its natural for an sc to burn a qaurt or oil i laughed

 

lol, did u tell him that its also common to find a prancing unicorn that somehow made its way in ur exhaust, poking holes

 

Before I got my oil changed a couple days ago I checked the oil level from the last change, and no oil was missing on the dipstick.

 

i worked at a ford dealership and they actually said that they would make more money just doing minor service then fixing cars with major problems most of the time they just lie and say nothings wrong so they dont have to do all that work to fix a car

but i would like to find out what this noise is just beacause of this noise i was planning on doing some serious mods this summer i decided that im going to use gm parts so i can keep my warranty reading some of the problems people have with their cobalts i cant afford to loose that warranty

 

u worked for fix or reapir daily/found on road dead

 

just a parts guy and yeah that saying is pretty much true

 

My 07 SS does the exact same thing. I asked the dealership and the manager told me that it was the fuel lines purging. I didnt know that when fuel lines purge, it sounds like someone locked inthe trunk knocking on the lid.

 

its not natural for a car to make a knocking noise regardless and these dealerships always just make up stuff so they dont have to fix it its sad we spend all this money on these cars but we get no help when we need it

 

When you turn the key to the on you are pressurizing the fuel system,you should hear the pump turning on.
You might be hearing piston slap because the fuel isn't getting to all cylinders instantly and the knocking is coming from the ones that are not getting fuel because the system is not pressurized.

 

well what do i need to do for this to stop i dont want to blow the motor or have other major problems

 

thats no good man !!! take it to the dealer!!!

 

Someone told me once that this sound was the fuel pump... He said it was common on any newer car to hear a noice like that. I didnt believe him, but Im also hear this noise every now and again.

 

if i'm understanding correctly, it's not a problem... it's just exhaust gasses... it sounds like somone is tapping on your trunk, and you looked behing you to wonder who the **** is sitting on your trunk, right? if that's the case, it's a totally normal sound and ntohing needs to be done