Every time after finishing a ride, if it's passed more than 15min, when I turn to ignition, the pump starts working but shouldn't. You can hear it clicking several times. What could be causing this ?
Says who? The pump is just pressurising the fuel in the carbs. After you turn off the ignition, the pump turns off and pressure leaks back through the system. After a while, could be 15 mins, could be an hour or more, when you turn on the ignition the pump will click for a few seconds as it pressurises again.
If the pump continues to run you have a fuel leak.
If you can smell fuel before starting the bike, you have a fuel leak.
If you have a fuel leak, it should be easy to find.