sounds like a fan needs looking after.
When my pc has been off for a while, like 6 hours it will make a lot of noise when turned on. This noise will not stop until i turn the computer off again.
I usually keep restarting the pc until the noise doesn't appear. Plugging in and out cables seems to help before restarting it. I thought the GPU was the problem but the problem is still there after installing a new one. I suspect it could be the power supply or the heat sink.
When the noise appears the pc will still boot into windows like normal, i can access hard drives etc.
No noticeable problems using it except for the noise.