Our Honda van’s engine makes a low intermittent hissing sound when it is cold. It is almost like a high pressure gas is escaping from a tiny hole, only when the pressure builds up to a certain point. We have not noticed that the hissing impacts on the performance of the engine or other aspects of the vehicle’s performance.
The sound comes from the lower passenger side of the engine compartment. It occurs during the first 5 to 15 minutes of being driven, and is more frequent when it is cold. It occurs predictably when the outside temperature is below 30 F and occurs sometimes if the temperature is below 55F. We park this vehicle outside.
We have taken it to our Honda dealership, and they have not had it hiss on them and they are unsure of what it might be.
Any guess as to what this might be?