What you should do depends on the cause of it. This usually happens after a computer reaches some age and you have used it for a while. It's usually a lubrication problem on the fan and can be solved by applying oil to the fan motor axis area where the fan rotates. You can use ABRO AB-80 but the sound might come back after some time. Personally I recommend sewing machine oil since that works great with fast moving parts. Alternatively you can also just change the fan. Make sure you have a professional doing these stuffs for you since you can mess up your computer while trying to do these. For the second part of your question, sorry I don't know any good place I can recommend for computer maintenance.