Occasional odd sound at startup
 

About 30% of cold starts (first start of the day, it won't do it when I leave work), I get a rattling or grinding sound. It happens when the engine revs up just a bit to 2k a moment after it starts, then the revs drop the moment it happens. It might do it a second time. I've got a few heatshield/other loose part rattles, but nothing too bad.

Has anyone had something similar to this been anything other than a loose part rattling?

I have the same thing happening with mine, it seems to be a rattling noise and it only does it for about a half second or so immediately after startup. Did some checking into it and found a tech service bulletin from gm that said it was the trans pump loosing prime when parked for extended periods. It would not affect anything and caused no harm. I did a flush and fluid change when I noticed it but there was no difference. I have driven the car for over 2 years now and the trans still works perfectly.

Flatlander

Could be the oil pump trying to suck oil for the first .5-1 sec the engine is started. My Bonnie dosen't do it but the Burb does.

When It's colder out I hear a quick(1/2 sec) grinding noise right when it kicks over. I have no idea what it is.

It will only do it if the revs to 2k. And won't rev that high until a couple seconds after it is running. So there is a delay between starting and the noise.

Perhaps the IAC is dirty or getting sloppy?