imac in sleep mode?

[ghostrider501]

hi to all,with the last 2days when i put my imac to sleep after a few mins it sounds like its doing something,the screen doesnt come on or anything and its not very loud at all,just a slight noise as if it doing something,then it might stop and later again i hear the same noise from it,so i was just wondering what this could be?nothing at all is running,i dont think,my imac is new,only got it at christmass and iv just noticed this with the last 2days,thanks to all for your help...
p.s even now i can hear the slight humming noise,

 

[Wassim]

I believe the noise you hear is coming from the fan.
Although your iMac is in sleep mode, it's not completely powered off.

i have the newest 27" iMac and i get the same thing, sometimes the screen even turns on and off after 20 seconds.

 

[ghostrider501]

I believe the noise you hear is coming from the fan.
Although your iMac is in sleep mode, it's not completely powered off.

i have the newest 27" iMac and i get the same thing, sometimes the screen even turns on and off after 20 seconds.

But why would the fan be on durning the night when the imac has being in sleep for hours?