Hi, so when I switch my newly built pc off, there is a slight scraping noise. I think it is the CPU fan, and i'm wondering if it does that because the fan stops as soon as the power goes off, whereas the case fans gradually stop spinning when the power goes off. It's a fairly quiet sound, but is it anything to worry about. Btw i'm using the stock fan
It could be a bad bearing, or it could be the fan needs to break in a bit more, or it could be that it's a bit loose and rubs at low RPMs. Hard to say. You'll want to keep an eye on it and if it persists consider changing it. Or if it stops of course you need to know right away.
It's safe to open up your computer and stop the fan with your finger (okay, relatively safe so you don't sue me).
If it's your CPU fan then either replace it with stock or consider getting a new Heatsink Fan combo.
I always get a large heatsink with 120mm fan. Read reviews and make sure it fits. Many large heatsinks don't even need fans as long as you have proper air flow (bottom front 120mm fan and top rear 120mm fan are best).