2012 Macbook Pro 15" Retina just started making "crackling/snapping/popping" noises.

I found a past thread that brought this up for newer Macbooks and it seemed it was the fan. I realize mine is older and would be happy if it is simply a fan replacement. Is there a way to confirm it is the fan w/o opening up the case? There is not a warranty to be voided at this point so opening, confirming and possibly doing the work myself is not an issue.