cold engine start tapping noise???

Sometimes when I start my car it has a tapping noise that sounds like valves or something. How bad is this and how can I fix it??

How long does it last for ?
Does it only happen on cold start ?

If it only lasts for a few sec's & less noticable when warm
then It's real common on these engines & nothing to worry about.
The oil drains from the hydraulic lifters & takes a few sec's to
refill. (altho I'm sure theres some much more technical explanations
out there :) )

Sounds like you know what I am talking about .. It last only a few seconds and quits. Good to know, thanks :D