It would be a lot easier to hear the sound if you used the laptop's internal microphone to record audio, and, if you'd quit talking during the video, heh.
Seriously, if you can tell for certain it's coming from the fan, it can really only be one of two things. Either the bearing is shot or the impeller shaft has broken or come free from the fan wheel and is slipping. Short of the motor failing entirely, those are the only two things that could really happen. If the bearing is failing or there is an impeller issue it's likely the fan impeller is rubbing against the fan housing or slipping on the impeller shaft.
Regardless of WHAT the issue is, replace the fan if you're sure that's where the noise is coming from. If the bearing seizes and shorts the motor out, you could have a serious issue with an overheated motor winding creating a fire situation or if the impeller busts free of the shaft you could end up with pieces of fan coming free inside the unit. Most likely it would just fail to turn the impeller at the speed of the shaft which would seriously impair its ability to cool the cpu or gpu.
Fans are usually ten to twenty bucks online and can easily be replace if you own a screwdriver and can follow the directions from an online tutorial which is available on youtube for just about every known laptop model made. Just google your laptop model and "disassembly video". It's not worth ruining a 500.00 or more unit over a 20 dollar max part.
Personally, it's very difficult to even really hear the noise well from the video, and from what can actually be heard, sounds a lot like an optical drive with an internal failure causing it to seek continuously, or a hard drive with a parking head issue, but again it's super hard to really get an idea of what you're hearing on the video.
Is the fan even circulating any air in or out of the vents?
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