So I just bought this APC BX1100C-IN UPS off Amazon. And while taking it out I accidentally pressed the power button, and a fan turned on, the power button wasn't lit up (which means according to the manual, the UPS is off), if I held it, it would light up. Anyway, the fan kept running even when the UPS was off for about 5 mins, then turned off with a click. Is this normal? Should I be concerned or return it or anything?