Super noisy whiny fan


Mac Ninja
I'm on a macbook pro 2 ghz intel core duo, and my fan just recently started whining and making really loud noise.

I think it only happens when my 23" cinema display is plugged into it.

I know this is just a hardware part failure, since this never happened before.

There seems to be two fans (right and left). Here's one:

I am ready to buy one of these now and install it. Question is... how do I find out which fan is faulty? My budget is VERY limited and I don't want to replace both if I don't have to.