Service transmission range switch and Neutral safety switch and you are good to go, it can be found under the gear lever housing(neutral safety switch) and on the transmission itself(Range switch). When you have removed the housing around the gear lever, clean all terminals.
The water sloshing sound is common and nothing to worry about, it goes away after the thermostat is opened.Its the coolant going around in the heater core. its common in Honda cities, airwave etc.