So i just bought a 750BQ and i plugged in everything in my pc.
Works fine when not under load and then when i start a game(under load) it makes a grinding/buzzing noise is it normal?

buzzing is always a possibility for the capacitors & such inside converting the power...but 'grinding' is pretty much a no-no. 

Could be coil whine, or even a bad bearing in the fan.

My money's on the fan. My 1000 GQ does a similar thing. Probably a wobbly fan.

Please contact EVGA technical support

I agree if it's grinding I would be doing an RMA since I wouldn't consider that normal.
 
Also it's worth warning that the warranty exists for a reason and the best way to get it fixed. Nothing inside a PSU is built to be replaced by the home user and they can carry an electric charge after they are turned off and unplugged from the wall.

 
RMA time.