clacking sound at start

when starting my '04 cavalier,as turning ignition on there is a clacking or rapping type sound coming from around the throttle body,something is engaging there as i start it.sometimes it has a small vacuum sound,almost like a very small backfire.car runs very smooth,and starts easy,just that rapping sound is wrong.what moving part is near the throttle body,intake that engages at the turn of the key(when the fuel pump kicks on) and prior to the starter solenoid kicking in?thanks

my understanding is that it is an ABS system check. if you have an owners manual, you might find out something in there. my 94 does it, and a 99 i have does it, also. it drove me nuts for awhile til i read about it. good luck! hope this helps!

I'd guess it's the IAC solenoid. Have someone turn the key for you and use a screwdriver as a stethoscope to find the noise.