I've noticed in the past week a strange knocking sound. About 5 minutes after starting my car after it's been sitting for a while, I hear this sound like someone's knocking on the roof or body somewhere. The first time it scared the **** outta me and I looked all around outside, but no one was there. After two or three times, I realized I wasn't going crazy. The weirdest thing about it is that it doesn't sound like it's coming from the engine, more like something is hitting the frame or body. Any ideas? Oh yeah, it seems like it happens when I come to the first stop of the car ride. And it's about 3-4 knocks, just like someone's at the front door.

 

i have the same thing on cold starts have no clue what it is. coming from the back of the car

 

Check your oil.

Try switching to 5w30 motor oil

 

Its a Cobalt thing. Nothing to worry about.


In the "Frequently asked Cobalt Questions" Sticky in the General section it says this:

Q: Do I have a ghost in my trunk?
A: Possibly, but it is more likely that the sound you are hearing is the trunk latch doing a self-test.

 

i doubt it has anything to do with oil. My throw out bearing in my v6 mustang is kind of noisy when it's cold out (in early morning starts or in the winter) and makes a noise that almost sounds like knocking, but i knew it wasn't right away. Eventually i found out what it was, it may be the same for you. start up the car and slide underneath and listen for it, find out where its coming from. It could also be a loose exhaust hanger making the exhaust tap slightly somewhere. This happens on alot of cars on cold starts because the rapid change in temperature expands the hangers and causes slight movement.

 

From what i heard guys it is just the fuel pump...or trunk latch as said!

 

Check your invoice, did you get the optional trunk monkey??

http://www.youtube.com/watch?v=8avOiTUcD4Y

 

i get that all the time, ever since day one, lol dealer said almost every cobalt has came in doing that, and no one has any idea what it is. lol

 

mine does it as im walking away from the car too. just a little quiet
click click

it almost sounds like the suspension settling after the weight of the driver is out.

i dunno.

 

yup, its like a "knock knock knock" or a "tap tap tap" seams to be coming from the rear of the car.....

 

yup thats the one!!!
its probably my suspension going
"oh thank god that fat ass is out *pops buttons on jeans* AHHHHH thats better"

 

yea i guess everyone gets it. first time i heard it i looked around thinking someone was trying to get my attention haha. But it does appear to become near the area where my gas cap is so i go along with the thought that its the fuel pump

 

I have heard it too , its the fuel system . First time i hear it i thought some one was knocking on the roof.

 

Thanks for the answers guys. At least now I know I'm not paranoid. I didn't think it was really a problem with the car, just wanted to see if it was just me.

 

It is the fuel pump. I was told this by GM directly.

 

Ok i can tell you right now what it is, supposedly our stock manifold expands when it gets warmer causing it to make a knocking sound...I replaced mine to get the honed manifold and took off my heat shield and it hasnt made the noise in about 2 months now

 

I've heard this on mine a few times too, mainly when at a complete stop. I wonder if its loud on the outside of the car. Wouldn't wanna roll up to a stoplight with a cop next to me and think I have a body in the trunk or something, lol. Good to know its normal though.

 

???

 

lol +rep , i missed that post .... WTF?