+1 to the above. Just because the fans are making lots of noise that doesn't mean they are working well - in fact it may mean the opposite. The air vents may be clogged, the fans dirty or even failing. Cleaning/replacing those will sort out the problem just as well as adding a new cooling system. Remember, the manufacturer designed the PC to stay acceptably cool during use, even at maximum load. If it isn't staying cool that is due to dirt or parts failure and just replacing those faulty parts will fix the issue.
Adding a better cooling system but not actually finding out what the real problem is may cause you more problems later as the faulty parts may fail completely.
I love my girlfriend, my dog and my canon 5DIII - even though none of them ever do what I tell them
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