Sorry if this has taken so long to answer. This post should have been made to the hardware forum. From what i understand of your post you run your computer without shutting it off. While you can do that with computers i see no reason to constantly run computers if they are not being used for something.It only takes a minute or so to startup the computer so there is no real reason for a home computer to be left on 24/7.
Now about the fan problem, the first thing i would do is download speedfan
and see what the temperatures are. Leave it running in your taskbar and when you hear the fans speeding up, check the temps. If they are higher than 50° then you should look into the problem. It may be that the thermal paste has dried up under the heatsink which is causing the heatsink to NOT work properly.
One caveat is that speedfan does not work on all motherboards so you may not get anything at all in the readings. You also may get some false reading from some sensors. I have one on this computer that reads -48° all the time.
let us know what the temps are so we can move on to the next step.