Fan goes wild.

[Linux for blind general discussion]

Hi!
On my old Linux machine when i have booted up or started linux i after maybe 5 minutes after booting up hear the fan goes wild.
It sounds like something is taking up big resources.
But this lasts for about 20 seconds and then goes down again.
Can i in the syslog and or in other logs as well find out if there is something in Debian taking up resources for a short while?
I don’t feel any lagging exept when i have loaded pages in firefox but that does not speed up any fans.
It is very confusing to me.
/A