Humming sound coming from roof top where water tank located / usually it happen when any of fauset tap is for about 3-5 minutes .

Not enough details to answer. How many units is this tank supplying? Describe the hum. Deep? High pitched? How long does it last? Just started or has it been around for some time? What valves are connected to the tanks outlet?
Give us something to work with here. Regards, Tom