My computer is Gateway P-6860FX. This problem started in the beginning of July. Sometimes I hear a loud noise. I believe it is the fan. It appears to be coming from the left side. Suddenly, the fan becomes very loud. Is this a problem?
YES. It could be several things but if the fan on the power supply of processor go out you could burn out the processor.
Check to see if there are any cables or wires that might be getting in the path of the CPU fan.
Run the system with the case off for a while and see if you can narrow the noise down to exactly where and/or what is causing it.
I'm recommending you to download cpu-z or pc wizzard programs and check your system temperatures, if cpu temperature would be to high, that will mean that your cpu fan is a problem, if main board temperature is too high than normal, then it would be caused by motherboard cooling system. And don't hurry to open your pc, cause you can clean the fan by using a vacuum cleaner. If not, you'll need to open it. Write me back if it helped.