You seem to have done the right sort of things, and now seem clear which fan is the noisy one.
A final check would be to roll-up a spill of paper (not floppy) but just stiff enough to stop the fan momentarily when running.
Do be sure the fan itself is really clean and if it is still noisy then replacement is called for.
The fine bearings when worn, can chatter as the fan speeds up and prevent it reaching full speed.
Provided you buy a matching replacement, it is not difficult to fit..... Just make sure that any nearby cables or RAM cards are not disturbed or at least well seated before you boot again. Miss this, and you will have more heart attacks when the computer won't run properly!