The rght side fan on my 15" is really noisy. Having removed the base, and turned it on, I can see they both spin instantly, but one is silent, while the other makes a fairly loud whirring noise. I've restored the OS, tried a PRAM and SMC reset, and neither have worked. I've installed istat and the left fan is actualy reading about 150rpm more than the right (left 2160, right 2010) but the right is noisy! Anyone know why this could be? I'd expect if they're both spinning at essentially the same rpm that the noise should be similar?