Question:
 
so i pinpoint where the knocking sound was coming out of after i shut down my PC.
 
it seems it's coming out of my power supply.
 
it's a 1000Watt supernova P2.
 
sometimes the knocking sound can be heard in the morning when i wake up, meaning it's been knocking for the whole night.
 
is this normal?

A knocking sound from your power supply is not good.  It would be best to contact EVGA support to discuss what can be done, possibly have an RMA issued for your PSU. Contact info is in the link below.
 
http://www.evga.com/about/contactus/

Mine has been doing the same thing for a year. I think it's the fan rubbing.