Since updating to Yosemite, my fan has been running slightly louder than normal. Also, there is a constant "loading" sound... the sound I expect when to hear when the computer is working hard to load something. It's similar to the high pitched, background drone of insects on a summer night. Certainly not loud, but annoying, as I've come to expect near quiet from this machine. When no apps are open, Activity Monitor shows nothing using more than about 1-4% of my CPU, but the loading noise and fan noise persist. While running Safari, everything is very slow and I see the spinning color wheel about every ten seconds. Activity Monitor says Safari is using anywhere from 30% to over 100% of my CPU? Any ideas? Thanks!