I am having a ticking or banging sound when ignition is turned to "on" in my 2008 LS. Zero issues with starting or power, has occurred intermittently maybe a dozen times over the last 2 months.
Almost sounds like it is coming from in front of the passenger seat, seems to be louder inside the car than outside and goes away after about 6 seconds. Engine starts fine even during the ticking noise. Any ideas?

HVAC cycling the trap doors. In some cars noisier than others. You may also hear the purge canister solenoid towards the gas tank after start up if scheduled for a purge. All normal in my car.

ahh i was wondering what that sound was. when i start my car after about 10 sec i hear a weird sound like something opening near the rear. Thought it was just the car warming up.
Thanks for clearing that up

Only thing i hear when i start my car (sometimes) maybe because it's on a hill, is some grinding like noise as soon as i start the engine. I doubt it's the trap doors spoken of here though

Does the noise go away once you put your vehicle in gear? I've noticed my personal car do this as well if it is parked on any sort of an incline. Have no insights as to what it may be, unfortunately. I see yours is an '09 - if you would like for me to check into its warranty status, please send me the last 8 digits of your VIN.
Regards,
Sarah
GM Customer Service

The noise only last like literally a second,I need to test it to see if it's because of the incline.

Sent from my PG86100