Strange Noise at Startup
 

This noise just recently started. It only occurs upon cold start and only for a fraction of a second just as the engine "hits" and begins to run. If you immediately turn the ignition off and then re-start, you can hear it again. The third attempt and you do not hear the noise.

The noise/sound is as if you have a small wheel on a bearing and spin it really hard with your fingers and the bearings are not smooth/aligned... it will "whirrrrr" for a bit then then go away as the wheel gains stability.

I know it is the sound of a bearing... but from where?

I had the inside cabin hatch off and started the engine and it doesn't sound like any of the pulleys related to the serpentine belt. I just replaced the water pump so I know it's not that.

Kind of sounds like it is coming from further back on/in the engine. Is it the starter...? Something else?

Thoughts?

Could be the water pump starting to go out. They leak a tiny amount that's hard to see before
they go out. Then the rattle.

Chain rattle is pretty common for a second or two on cold start up. The SAI pump has a bit of a whir to it as well, but it lasts for a few. Could possibly be the alternator pully, or maybe a tensioner, but I would think those would be more persistent.

My 03 does the same on cold start.

noise
 

I sometimes get a whirring noise upon engine start that begins just a the engine fires up and it quickly goes away.
My mechanic suspects I'll be needing a new starter sometime. So far it is intermittent, maybe once every 30 starts.

Thanks for the replies - not the water pump - it's brand new. I was considering the starter too. Not timing chains... unless it's a gear that spins with those. Doesn't appear to be any of the serpentine belt pulleys as it didn't sound like it was coming from them with the cabin engine hatch removed.

For now, it sets until spring. 4 inches of snow last night and it has its blanket over it with the battery tender plugged-in.

Are sure you aren't hearing the AIS pump? It runs when the engine is cold and pumps air through the cats to reduce pollution. It can emit a whirring or whining noise for a short while.