I replaced the power supply and the noise stopped! However, I still hear a pulsing sound, that I'm guessing is the fan on top of the CPU. Could you please tell me what the correct fan is, how to clean the heat fins and or how to replace the heat sink and fan?
I suggest that you do a thorogh cleaning inside and out of the case. You can use canned air to carefully blow the dust out of the fans and other components. Also, using a small brush will help remove the dust from the fans. Dust in the fans will cause many problems. Here is a guide to help you with the cleaning.
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