When was the last time you opened it up and cleaned the dust from everything, including all cooling fan blades and heatsinks?
I couldn't really get anything from your first video but the second one sounded like something is touching the blades of one of your fans as it spins. You have to isolate which fan this is coming from if you can, it shouldn't be too hard really.
I had a unit once where a part of a plastic guard inside the power supply unit had loosened and was being hit by the fan. It was a simple fix but opening the PSU case voids any warranty (if it still has one).
Without physically being there ourselves, it's impossible for anyone to accurately track just where this is coming from really, you'll have to try yourself. One suggestion that could help is to take any kind of flexible tube and while holding one end to your ear, move the other end around different parts in the case. You will hear the sound loud and clear when you have the tube in front of the object in question. This is an old trick from the mechanic days to find engine knocks with a piece of garden hose, it works very well actually. Then you just have to find what's in there that's causing this noise or if it's a bad bearing/bushing.