Probably air caught in the cooling system. Be sure the small hose between the radiator and the coolant reservoir fits tight and in good condition and that the reservoir is full. The check valve in the radiator cap may also be faulty, replace the cap if in doubt. The system is designed to bleed itself of air if all the components are good.
Chevy installed a water restrictor in the heater hose fitting, It is designed to slow the water flow up a little so it won't make that noise. It has probley decayed away. It will not hurt anything. It just makes that noise.
You may have water somewhere in the bottom of your trunk. If not, it could well be the sound of your gasoline sloshing around in the tank - older GM cars were notorious for this sloshing sound.
I have seen the doors with inches of water inside because the drains were plugged up. You could hear the water sloshing back and forth while driving.
Hearing under water is easy, although speaking under water is difficult. Water conducts sound quite well, better than air does, in fact.
Because your fail
Because it's not like it's a jug of water down there! Sometimes you actually can hear ut
If the noise is coming from the dash, your condensation drain is clogged. under the vehicle, passenger side at the bottom of the a/c box is a rubber "udder" reach up and squish it to open it up and drain out the water. p.s. wear a raincoat...
The thermostat on a 1989 Chevy Celebrity is located under the water outlet fitting. Follow the upper radiator hose, it will end at the water outlet.
Water may be getting stuck in the convertible track.
you got water under the distributor cap
clogged drainage hole in the cowl (under the wipers)...
Jamie started to feel nauseous as she looked over the side of the boat at the ugly black water sloshing against the sides.