My wifes car,we bought it new , now has 145,000 miles on it ,no problems till tonight coming home,never had any issues with the car. while arriving home ,shut car off,notice this noise,open hood ,this thing is perking like a old coffee pot.temp. guage stayed in middle the whole time,elecrtic fan is working,runs like a swiss watch.let it cool down ,coolant level low,appox, about 3/4 gal ,did not any drips under car except what came out of overflow tank,any ideas?

Fan may not be running on both speeds.

3/4 of a gallon is A LOT of coolant loss. Fill it up and keep a V E R Y close-eye on it! ....and bring some spare 50/50 mix with you uNtil it is fixed.

You could have a leaking water pump or a toasted head-gasket.

Check the radiator cape and the thermostat. I've gone through two caps on mine and when I did my water pump and timing belt, I found that the thermostat was broken. It's also very hard to get all the air out of the system once it gets in. Find a shop with an Airlift system to bleed it.