Noisy...

My laptop is about 6 years old. Until the last couple of months it has worked really well. Lately it is sounding really funny and I am confident that something is about to fail in it. After running for several hours it starts making a really loud sound. We have had to take it apart to clear dust out of it which usually makes it work fine. This is now not even working which makes me think that the sound is a part that is going bad. I have started looking for a replacement but am trying to keep this computer as long as possible. It serves my needs and I don't want to spend money that I don't have to until I am forced to do so. It would be really nice to get another 6 months or so out of it.