When i drive my car cold i hear a rattling noise on the drivers side under the hood??

The sound seems like it's right near the fire wall on the drivers side BUT ONLY HAPPENS when the car is cold never when it's warm and it just started doing this... I usually NEVER drive the car when it's totally cold i usually warm it up for about 10 min untill it breaks 130 them i drive... But i have been in a rush a few times and didnt have time to warm it up and get this rattling noise as if something might be loose under the hood.. The sound ISNT at idle but when i strat driving at no particular points in the powerband i'll hear it breifly then it will dissapear and come back MAYBE when i shift (only sometimes) then go away. It's NOT a consistant rattling which leads me to beliebe that it might be something loose but why then does the sound dissapear when the car is warmed up about 145???? Maybe because when the car is cold everything in the engine bay is contracted (due to the cold) and when it warm up it expands just enough to make whatever's loose snug so it doesnt rattle but i'm just floating this.....Any ideas what it could be???

Probably Piston slap. Just about every f-body has it. I'm very lucky one and don't get it. or maybe its because I only run synthetic oil? I dunno.

It doesnt matter if you let your car warm up without idling. A lot of people actually say its better not to let the car idle for long periods of time.

Or a lifter

it's defintaly not a lifter...i know that fuckin' sound....

idle or not, it's a car, guys.

I'd say drive around and then pop the hood and rev it with the throttle body. see if you can pin point the sound and see anything moving or hear something.

You know whats weird also that i just noticed when attempting to figure wtf the noise is....

I took the car out totally cold and it is dark out.. so obviously i had my headlights on... Now when shifting into 2nd after i made the shift i heard the noise for a quick second and when i heard the noise i noticed that my headlights got dim for a split second then went back to normal (kinda like a quick flash) so do you think that has anything to do with it??

Maybe alternator bearings? I have heard they make a rattle when going out or losing lube.

It's a possibility that it's the A.I.R. pump. If I understand correctly the pump runs when the car is cold to help light the cats off quicker. I had a similar noise on mine until I did the !A.I.R. mod. Just a thought.

Try doing this without driving. Just use the throttle to get the motor reving some. If it does not make the noise at all then more than likely it is a suspension issue. I had a deal sort of reverse where after the car warmed up I started to hear somewhat of a knocking noise on the passenger side front. Looked all over and could not figure it out. It turned out to simply be one of the new ball joints I put in went bad. It was not a constant noise but frequent. Anyway, at least if you do a test without the car moving and it does not make the nosie you are removing the motor since it is always moving even when in park. Only when the car is moving will suspension come into play so I would try to start there.

Sounds like a plazn i think i will start out by checking that out and hopefully i will find something b/c it's driving me nuts!!

Well I got the same sound but mine is only on a cold start and mainly only if i'm low on gas and hit the starter quick, but it doesn't start and I hear the rattle then. NEVER heard it while driving. Its not in the engine though it is definetly somthing rattling against the firewall. Mine started after I had my cats taken off. I think maybe the sound was always there but without the heatshield of the cat it maybe is more audible now. I dunno, your not crazy though :)