When I start my car, or shortly after, I hear four distinct knocks from the rear of the car. It lasts about a second. Only does it once, and it can be heard from outside. Wondering what that is. I'm sure its normal. Hopefully.

 

It's your fuel pump, mine does the same thing occasionally.

 

it does it when your driving? or just sitting?

 

repost... search

 

thats wierd, never heard my fuel pump makin lound noises...

 

holy ****...i have been wondering what the hell this was for so long. it happens randomly in my car. sometimes every other day, sometimes not for a couple weeks. at least i know its something normal now

 

wow thanks I was gonna post something about it but thought it would be a dumb question now i know.

 

Ya its your fuel pump doing a check. It does it more when it is cold outside (well at least for me) The first time I heard it I got scared, I thought someone was knocking on my back window. Now I tell people that my car knocks at me to say hello.

It is normal though so don't worry about it!

 

Thanks all. I tried searching, it was very broke at the time.

"repost... search"

Was is harder for you to tell me to search for it, or be silent? You chose to waste time posting dumb things, not me.

 

I was always under the impression that it was the trunk doing a self lock test or somethin.

 

We call it the "Evil Trunk Monkey". It is completely normal. If you stand around your car after you shut it off, about a minute later it does it again.

 

same thing hapends to my car i thought it was something under the rear bumper loose or somthing

 

That's weird. When I start my car it's a cobalt. I don't get it.

 

Yeah happens to mine to. Nothing to worry about.

 

It's not the goddamn fuel pump. Fuel pumps whine, not knock.

It's your trunk lock doing a self-test to see if the trunk is ajar. Completely normal, my car does it as well. It's more noticable if you have the seat folded down like I usually do.

 

^It isn't the trunk doing a check. It is the fuel pump doing a check. I read up about it on more than one site and even the machanic said. It does it more when it is cold for me and yes it does it when I turn the car on and when you turn the car off it does it as well.

 

What are your sources for this? What mechanic? Just because somebody is a mechanic doesn't mean they know everything about a certain platform of cars. I know people on here who aren't even involved in the automotive field yet they know more about these cars than your average GM tech. I so happen to be one of them. Not bragging about myself, just staying facts from what I have witnessed in the real world. I have talked "Cobalt" with SEVERAL "Certified" GM technicians, and I knew a hell of a lot more about the Cobalt than they did. One tech didn't even know that the SC uses synthetic oil from the factory, and should be changed as such. Joke.

And I stand by my previous statement. Too many people relaying false information, which in turn people read up about and think is the god-honest truth.

 

I have had my seats down before and the sound is not louder. It the same if my seats are up or down.

 

I actually retract my previous statment...partially, anyway. It's not the fuel pump, but it's also not the trunk...apparently, it's the evap canister self-test. Found elsewhere on this site (by searching, no less) -

Document ID# 1890375
2006 Chevrolet Cobalt



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Subject: Noise from Rear Of Vehicle - keywords canister cold CVS click evap knock L61 LE5 noise rear solenoid tick vent #PIC4317B - (01/23/2007)



Models: 2006-2007 Saturn ION

2006-2007 Chevrolet Cobalt

2007 Pontiac G5

2005-2007 Pontiac Pursuit

with Engine RPO L61 or LE5




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This PI is being superseded to update technical information. Please discard PIC4317A.


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The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
A noise may be heard from the rear of vehicle; typically 3-5 knocks during initial cold start. The noise may sound like someone outside of the vehicle is tapping on the back window or on the rear exterior body panels.

Recommendation/Instructions:
This noise is from the vehicle's EVAP canister vent solenoid going through the diagnostic cleaning cycle, which is part of the software calibration set-up. Replacing the EVAP canister may not resolve the issue when the vehicle is re-exposed to a cold start. No parts should be replaced. This should be considered a normal condition for 2007 and previous model years.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.




I've noticed my 08 makes a similar, although much quieter sound. Sounds like they addressed to ease some minds.

 

"with Engine RPO L61 or LE5"

They didn't mention the LSJ, however. I have an LSJ-powered vehicle and I still hear it. Sounds like it is most likely the source of the noise.

 

^Yes, thank you and yes I was wrong. I will admit that. But there you go, that is actually what it is....either way it is normal for the car to do it.

 

Looks like I was wrong as well. The bulletin didn't mention the LSJ engine, but it is most likely the same thing making the noise. Next time I start my car when it is cold, I am going to place a microphone next to the latch, and see if it is the source of the sound.

 

for me its the person in there knocking to get out, hes been in there for about 3 days, in about a 2 weeks or so he wont be making noise anymore

time=problem solver

 

thats the tied up hooker u left in the trunk. Better take her out before she ruins the upholstry!

 

Get to it!