Windows 7 - How does adding more fans help?

my brother installed a new fan in my computer (it has 4 fans now)..and i noticed that one loud grinding sound that used to come when the pc was powering up is heard less after installing the new fan..(the DVD rom's sound)..
so i want to know how adding more fans help the computer..and why is the sound so less now?

Possibly the fan that is on the way out does not have to work (spin) so fast. More air = less heat....to a degree.

thanks for replying Doofus.
the thing is, the DVD rom doesn't work the right way. like, i have to push a pin in that small hole and then it ejects the box. and before installing this new fan when i used to start up my computer,say after 8 or 9 hours there used to be this grinding sound from the cpu (in my guessing it was from the DVD rom, cause its spoilt) that sound is less now. what would a new fan have to do with lessening that sound? (or was it never the sound from the DVD ROM?)

Fans possibly don't have anything to do with it. It's probably a warning to track it down & replace it. One day it might go POOF!

You need to locate the source of the noise. It could be a fan going bad. It could be your CPU fan and with the additional fan the CPU is running cooler and its fan does not have to spin as fast. Just a guess, but I would try and locate the source of the noise.

Jim

yup., my friend had told me that the DVD ROM has a problem and it makes this loud noise when starting up

I will be getting a new one soon hopefully