Do you hear it when you come home, park and turn off your Ascent. If so then that is normal, I believe. I forgot the mechanical process that is taking place, but Robert.Mauro the moderator or another member can explain.

 

Hi. I hear it with the engine still on. I’ll put it in park and walk back over to the rear wheels and hear the hiss hiss hisss hiss. Ill turn the engine off and everything is silent.

 

Not to worry. There are lots of very nice and experienced members on this forum. Most are probably sleeping now, but by tomorrow I'm sure you will have a lot of help in determining what is happening. Stay tuned!

 

Ok. Sounds good.

 

The normal hiss happens 8-10 hours after the car is shut off. There's a process that purges the catalytic converter. Worried me like crazy first time I heard it until I googled and found out what it was.

Since this happens while the car is running and stops when it is shut off, that sounds more like a pinhole in the exhaust system. I'd have it checked out.

 

Hmm. I noticed that I hear a sound like fluid running through a line as soon I press the ignition button before the engine even turns on. I hear it for a few seconds right before the engine turns over. Once the engine starts and is idling, I hear the same noise but only sputtering. It stops sputtering and goes strong when giving it more gas.

 

Do you have the air conditioner on? There's a rear drain and tube in the back that could "hiss" and sputter.

 

Correction. It still hear sputtering even when I give it more gas while in idle.

 

Can you videotape it?

 

Does anyone use tape anymore? ? ?

 

ok.

 

Snakes why is it always snakes! ?

 

Perfectly normal. It's mentioned in the first couple of pages of the manual and can happen up to 10 hours later. I forget what it's called. (fuel vap system check??) Glad I read about it first. I heard it in the evening as I checked to make sure the garage door was closed before going to bed. This was about 5 hours after turning it off.

 

I'm glad i read this. I have the same concern although it sounds more like a small air compressor or electric pump. Ill have to dig through manual. I notice if turn the vehicle on and off, or even set to accessory, the noise stops. Is this the same thing?

 

Hi. The sound is with the vehicle on. I hear it underneath the car right in front of the rear tires. Its not the sound that comes on hours later after turning the vehicle off like in the manual. Its most noticeable in a garage, which is where I heard it first.

I took it the Subaru dealer and one of the master mechanics said it was just the cvt regulating the pressure. I asked if its going to hiss all the time and he said “yes”. Weather doesn’t affect it.
We took it for a test drive and everything sounds ok and checks out. ?

 

The sound while the car is off is normal. Disconcerting, but normal.

The OP is hearing a hissing sound only while the engine is running.

 

I heard the same noise today on a brand new Outback with 270 miles on it. Its not as loud as it is on the Ascent but it is there. Normal Cvt noise. ??

 

I'm glad that you have some satisfactory resolution from the source, so to speak and I hope that your understandable anxiety is now reduced. Cars in the 21st century are quite the marriage of mechanics, electronics & technology, aren't they! We went from "purring like a kitten" in the 20th century to "hissing like a snake" in the 21st! May you and your Ascent share many years of happy adventures together. Safe travels! (Does he or she have a name, yet?)