I can hear something like a hissing, or a pressure relief coming from the drivers side every minute or so. It will hiss/vent every minute no matter if it is in gear, or in neutral. I had the HVAC turned off, so it isn't anything related to that. The only weird thing that has been happening lately is the car is moderately overheating. It used to stay around 1/3 on the temp guage, but lately it goes slightly over half. Any ideas what that hissing it? Thermostat?