Well it is certainly a weird noise. Sounds sort of metallic maybe a hard drive fault? Have you got a disk in your optical drive?Failing that maybe a fan. It definitely sounds as if it's coming from something spinning to me.I think you need to try and eliminate any possible causes by removing power from them and see if it stops.
Well you can soon disconnect the system speaker to check that.
Unless you resolved it already, try and disable C3/C6 state in Bios. That could work, as reported on other forums.