i have 2000 jeep grand Cherokee limited 150 k miles on it

i replaced the radiator 2 times and i started having problems.

everytime i hit the gas there is a water running noise under the passenger seat and my heater doesnt work quite well .how ever eveytime i hit the gas and hear that noise i get hot air.

eveytime i check the coolant level in the radiator its seems like its less.