Have a 15'' rMBP 2.7/16. The fan speed on my laptop speed seems irregular from times to times. Not often, but sometimes the fans ramp up to full speed (6000rpm) even though the temperature may be only in the 50sh (Celsius). Stays at full speed for some seconds and then lowers to normal speed. On these occasions the load is typically relatively high, but the temperature is not high as far as I can see (use iStat and SMC fan control to monitor temp and fan speed). Normally the speed is low however, even under high load, and does not increase until the temp is approaching 100 degrees. I have tried to reset SMC with no difference in behavior.