Why is my computer so loud?

I've had this HP desktop for about 3 years now but probably in the last 2 i've had this problem. Its not the cpu fan because i had it cleaned out by a computer shop about 3-4 months ago and i just cleaned it about 3 days ago. It only makes the noise when i play games or do a lot or heavy stuff. If it makes the noise for about 30 minutes straight it will just power down. No warning, nothing, it'll just shut off. When i turn it back on again it only takes 20 minutes to just shut off then lower and lower each time, so eventually i just have to shut it off and leave it for the day. I've been doing a little research and am thinking its the hardrive. What do you think?