Intermittent hissing sound

Hi,

I got out of my truck this morning after driving to work, and there was this intermittent hissing sound like air was escaping from somewhere.

Does not seem like it is coming from any of the tires.


Also lately my truck has been feeling kind of floaty on the road, and there are times when I'm turning and my back end feels like it's drifting on ice even though I'm not.


Thoughts?

 

I’ve heard this on mine as well. Pretty sure it’s the ac. Haven’t thought much of it. My headlights hum as well.

 

yeah but I was running me heater this morning

 

The ac runs in defrost mode.

 

Could also be the fuel pump depressurizing.

 

take 'er to the dealer see what they say

 

“Toyota says it’s normal”

 

The wife's Chevy traverse does this constantly, hvac system turn it off and it goes away. Chevy says it's normal for the system to de pressurize. Haven't noticed it on my taco.. How can it be normal if not all cars do it?

 

Not all cars have the same systems

 

A/C systems have two sides. The high pressure side (Condensation) and the low pressure side (Evaporation). These two sides are separated by the compressor and a controlled orifice. While operating the high pressure side will reach as high as the 250psi range while the low pressure side will be in the 50psi range. When you shut the system off the refrigerant will pass though the orifice to equalize the pressure. It could be possible to hear this when it happens but I have never even on the massive systems that I work with.

Edit @Skydvrr 's answer is so much simpler. And what I am trying to say.