Hi,
Noise 1:
I got in my car (04 MC SS, 23K miles) this morning and started the engine. Just before the engine started, I heard a loud knocking sound from under the hood, sounded like rocks in a tumbler. It sounded closest to the left side, but not exactly sure where it was coming from. I stoped and started my car three times, and each time it did it. It drove well. When I got to work I did the same thing, stoped and started, this time no noise. I am assuming this is a "cold start" issue.

Noise 2:
When I was would accelorate at high speed,I noticed a rustle sound, like leaves getting mulched. I had the AC and Radio on. Not sure where it is coming from.

Has anyone experienced this?

Thanks,
Ralph

 

Sounds like detonation, Just a guess not a 100% sure, but heres a link. My dad had the same problem in his pickup.

http://www.contactmagazine.com/Issue...ineBasics.html

 

By chance is the check engine light coming on when the noise is there.
Is the noise there all the time, or when you first start it when it is cold

When was the last time you checked the engine oil and coolant level?

Possible headgasket leaking anti-freeze on top of the piston
Possible rod knock as well.

If the check engine light is coming on, run by AutoZone, They will hook up a scanner for no charge and will tell you the codes