sorry, should have given more detail...i was still half asleep.
All the drives are internal - 3 + SSD attached to motherboard and 4 attached to PCI controller. I didn't install the PC speaker (and I don't think there is one built into the motherboard, since there is never a POST beep), so I'm pretty sure it's not from any other device. Also my best guess is from the fact that I hear a seeking-ish noise right after each beep.
I did notice that video cards can beep so I'd better check that too, but the seeking noise feels related so I'm leaning towards hard drive. A few drives are connected using molex adapters so I'll also check that (X460 natively has only 5 SATA plugs).
Unfortunately that link's youtube video is dead, but based on the following links my problem is different. My beeping is at random times, i.e. it might cluster a few beeps ever few seconds, then not beep for awhile (e.g. 30mins) then beep once or twice, and then not beep again.
http://www.youtube.com/watch?v=-06b0Uxcj2Q
http://www.youtube.com/watch?v=xXxtSUwC2wk
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