Recently my 11" MBA (Mid 2011) has started running the exhaust fan at high revs continually. It starts about 20 seconds after boot up and continues at the same high speed until the notebook is shut down or goes to sleep. It does this regardless of what is running and Activity Monitor shows no CPU or memory usage to cause this. I've also monitored the temperatures and it isn't running hot. I've uninstalled everything I could and even reinstalled Mountain Lion. No luck there. Everything seems to point to an SMC issue and the issue does seem to coincide with the latest SMC update that was to fix possible battery issues. I've tried resetting the SMC (following Apple's instructions http://support.apple.com/kb/HT3964) about 20 times with no luck. Any ideas what it could be? Cheers.