91 gc cooling trouble

:banghead: I have a problem with my 91 grand caravan 3.3l. while driving in colder weather ( 20-40 degrees) my cooling system i think is making a squealing sound and builds up pressure in the system. the noise stops when you slow to about 10 mph or so and is not there with the car idling. the problem does not happen in temps above 40 degrees or so. i've changed the water pump twice thinking that was the problem and the thermostat. the temp on the dash guage drops from 1/2 to 1/4 when this happens. any help would be appreciated. thanx

It sounds like either a bad or worn belt or a pulley. I don't recall a cooling system causing these types of symptoms you have encountered.