I've got a wierd problem with my PC. When I cold-start it in the morning (room temp about 15 deg celcius) my CPU fan is really loud and sounds like one of the ball bearings is damaged. The noise stops as soon as I login to Windows. It's a stock AMD Athlon 64 3000+ fan. Is this common or do I need to get a new fan?

Get a new fan. IMO, any time a fan makes noise, it should be replaced. They are very cheap and you don't want to wait until it stops and fries your CPU.

Could be something to do with voltage, it sounds like its charging up like a mother when you turn it on. But new fans are cheap, so you could get a new one. One thing: Are you sure its the CPU fan and not the fan in the PSU? AMD Athlon 1.8GHz 512MB RAM 120GB HDD SATA 12GB HDD IDE GeForce 4 Ti4600 w/ 128MB RAM Pioneer DVD/RW SB Live! 5.1 ABIT NF-7S Mo/Bo

Sounds to me like the fans speed may be software controlled so it just runs flat out until the controlling software loads and then slows it to an apropriate speed. I agree with ham30 though, if in doubt replace it, it's not worth the risk.

Why is it that people look for complicated answers to simple questions. When was the last time you cleaned the built-up dust and crud from the fan? You can also carefully lift the adhesive sticker from the bearing and add a drop of light machine oil (sewing machine oil) Be aware it might not be the CPU fan. Most pc's have fans in the powersupply and possibly on graphics card and/or northbridge. It is common for a fan to be a bit noisy at cold start and to quiet down after warming up for a minute or two. It is a sign of normal wear and will eventually need replacing if the simple servicing/maintenance described above does not solve it. Give a man a fish and you feed him for a day. Teach him to fish and his wife will never forgive you.

Yeah, fans become noisy as the oil dries up inside and the bearings wear down. I usually take the sticker off carefully, remove the rubber plug, and while the fan runs, I apply 3-in-1 oil--several drops, and even teflon grease as well. I put in as much oil as I can, and am careful not to apply too much. I make sure there is no oil outside the hole and wipe it with alcohol if needed. Put back the rubber cap and then wipe again and put the sticker back. The fans can last for quite a while longer--months and months. In fact I have a fan that I have kept running for a few years already with only 2 oil treatment. I actually like to take the fans out completely and connect them to a 12V supply so I can spin it up, add oil, stop it, move the blades around--work the oil into it really good, add the grease and work it into it, etc... Tek.