2003 Civic noise on overnight cold statup?

Hi!

I have a '03 civic ex w/ the 1.7 vtec engine that sounds like it has a
slightly extra noisy valve train chatter on startup when initially started
in the morning. It goes like this: I start the car and the RPMs jump up and
come down to rest around 1000 RPMs and this is when the noise is heard. The
RPMs will SLOWLY get to about 850 RPMs all while the noise is still heard.
Suddenly, the RPMs jump a tiny bit, to about 900 RPMs, and the slight
chatter noise from the engine is gone.
This slight extra chatter only happens after the engine has been off for
about 6-8 hours to the best of my knowledge.
Is this normal? Does it happen to anybody elses civic?

Thanks in advance!
Chris

 

Could this be the ABS pumping up? That happens every time you start, but
might only last long enough to be noticeable after the car sits for a
while.