Good morning,
The noise is the coolant boiling in the heater core from the coolant being too hot.
https://www.2carpros.com/articles/how-an-engine-thermostat-works
I would start with a thermostat replacement as it may not be controlling the temperature of the coolant.
https://www.2carpros.com/articles/replace-thermostat
I see no Liberty listed for 1999 so I looked up a 2009 which is the same for all 3.7 engines.
Roy
Do not waste reusable coolant. If solution is clean, drain coolant into a clean container for reuse.
If thermostat (3) is being replaced, be sure that replacement is specified thermostat for vehicle model and engine type.
1. Disconnect negative battery cable at battery.
2. Drain cooling system See: Cooling System > Procedures.
3. Raise vehicle on hoist.
4. Remove splash shield.
5. Remove lower radiator hose clamp and lower radiator hose at thermostat housing.
6. Remove thermostat housing mounting bolts, thermostat housing and thermostat.
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Sunday, April 21st, 2019 AT 8:13 AM