|When system gets so extremely slow I guess, all files you're burning will be scanned for viruses at the same time.|
This might result in a 100 percent utilization.
In this case, the CPU fan and the fan of the power supply should run faster. In most cases the noice increases, so that you directly can hear this.
I could be a problem of high temperature.
You might have to open the computer case and take a look at the heat sink. If it is full of dust, you have to clean it. That might solve your problem.
Please send a reply, if you solved the problem !!!