Have a 2006 Highlander AWD Limited with about 150K on it and all service done. Now there is what sounds like a coolant gurgling noise behind the instrument cluster (or thereabouts), which could be air in the system. But when pressing the switch for front defrost, the noise disappears. Hitting the switch to turn front defrost off bring the noise on again. I would have thought that the front defrost switch changed air routing but not coolant routing, but the noise sound liquid and not like air. Ant more clues or things to check?
