OK..im not too car savvy alright but ill do my best..my 1999 camaro v6 was brought to california from chicago in about 2002 ..i bought it last november with about 33XXX miles on it..have done oil changes, kept it clean, had it for about a year..havent done any upgrades, still stock..now the car is at about 420XX miles on it..heres the situation...when i turn the car on..after a minute or 2..maybe not even that long..it will began to make a high pitched noise..it sounds to me, like little b.b.'s in a soda can..a friend of mine told me that it is that catalytic converter and it happens from leaving your car on for long, or running low on gas..i do those things by accident, more often than not...my question is that iF this is true..how can i fix the noise..do i need a new cat..what else goes with a new cat. convrt. PLEASE HELP...I DONT LIKE THIS NOISE..ive tried using the search, but found nothing on the ball bearing type of noise...thank you maro heads belated thanksgiving ya diiiiiiiiiig

 

Could be a heat shield over the exhaust.

I would get under it and see if there is anything obvious there. If you don't find anything then explore further.

 

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this sounds to me like the heat shield on the cat. rattling. try listening under the passenger side right under the door. if you look under there you'll see the cat and right above it is the shield and at low rpm's the shield will sometimes vibrate against the body. if you determine that to be the cause the easiest fix is to put a piece of cork ghasket tween the shield and the body.... I hope this helps.