It's most likely the console's system fan. Since it seems to be a common problem, I wouldn't worry about it too much, but if you're really concerned, there is a course of action that you can take. The first thing that I would recommend is lubricating it with a mineral oil, don't use WD40 for this. You'll need to disassemble the console to the point where you have access to the top of the motherboard, such as step 10 of [guide|22231|this guide]. I can't tell from the pictures, but it looks like you can remove the plastic fan assembly from the heatsink. Do that, and then use [http://www.dansdata.com/fanmaint.htm|this procedure] to lubricate the system fan. That should quiet the fan down and possibly extend it's life.