I had heard it very faintly before, but lately, it has been running louder. I'm not sure if it is any faster than before though, or if the motor is louder when it's very cold. I haven't experienced any high temperatures with mine, more than 1 degree different than any other, but it is usually lower. The 5n1 is just slightly high 3 F in the day, but at night it can be 5 F too low compared to all others in the 20F or less conditions.