Fan rattling - not sure if I need to replace right or left.

Dumb question. My fan has been rattling for a while and I've had it. I know which fan is making the noise. There's nothing lodged in it and I think it needs a replacement but I'm sure if it's the right or left... it's the left side fan when the computer is open and I'm using it, but when I flip the computer over to open it up... it's on the right side.

I just don't want to buy the wrong part is all. Sorry for the dumb question.

Edit -- also if I buy one, will it act as an OEM normal part? Can I still see/change my fan RPM's etc?