I have a 2008 IS250 and have a clicking/rattling noise when I start my car. The noise only last for a split second. I have tried keeping the AC off but it still makes the noise. Here is what I have noticed everytime I hear the noise (which doesn't happen all the time).....winter/fall time happens when it gets close to the 3 month mark for an oil change, happens more often during summer time when the car has been parked for less than an hour/hour and half plus when it comes close to the 3month mark for an oil change. Has anyone else had/have this problem?

 

If you can take, and install the serpentine belt.

Remove it, and spin all the pulleys. Check the idler puleyes for play. Also the belt tensioner see how easy it is to move.

Other than that see if you can post a video. Upload to YouTube and then post link here.

 

Serpentine belt and tensioner was replaced last year and still having the problem.

 

This sounds EXACTLY like the symptoms fixed by the cam gear recall on the IS350. (yes, I know you have an IS250, but...)

Listen to the noise that the camry in this video makes:
Is that the kind of sound you are hearing?

 

I'd start checking your oil level at least once a week or more during that last month.