Hi. I need help. A hissing sound is heard from the back of the car while driving. A sound similar to a compressor pushing air into a tank. This sound is not affected by the running of the engine or the brakes. The sound starts from about 20 mph. The hissing is best heard when I drive the car and put it in neutral and let off the gas. Does anyone have experience? Thank you very much and please excuse my english.

 

A Snake in the Trunk! Must Be a Cobra Mustang!

Welcome, Just Kidding!

Get a Buddy To Sit in The Back and Try & Narrow Down! Also Try Coasting with Engine Off & See If It Still Makes Noise. Check With Both Ignition Off & On As Well! That Will Tell if it Is a ROLLING Issue Vs Engine Running Issue! Find a Safe Place & Don't Let Steering Wheel Get Locked on You! Could Be Rubbing Issue or Vacuum Pressure Issue With Emission Hoses Etc.

Might Also Check Out This Thread!

https://themustangsource.com/forums/...p-link-550939/

KC

 

I'm already trying, it can't be identified. It's definitely doing something in the back and the engine doesn't affect it. Not even the brakes. The only thing I can think of is something around the differential or the emissions.

 

If You Still Have Your Gas Can Adapter For The Fill Neck Try Inserting it to Depressurize Tank. See if It Makes a Sound Change.

Kc

 

This Pic May Help in Your Brainstorming The Location of The Noise! 2012 Boss 302!

KC

 

I tried. There was no pressure in the tank. Another idea? 😁

 

Have You Tried Putting up on Jackstands And Running in Gear! Place Well & Be Safe! Have a Helper in the Car to Hit The Skids if Needed Don't Do By Yourself!

Have You Checked For Any Dtc or Body Codes??

Pm Me a Vin & I Will See If There Are any Ssm's on it. That is Ford Special Service Messages For Various Issues!

Also Some Pics of The Car Might Be Helpful!

How Many Miles on the Car??

How Old Are The Tires??

Rusty Exhaust System?? May Have Pinhole Somewhere??

That Big Rectangular Black Box Under The Spare Tire Well is The Emission Stuff, Might Pull & Give a Look See if Any Hoses are Split! Be Mindful of Disconnecting Hoses With Proper Tools & Gently Handling As I Imagine Replacements Would Be Difficult For You To Locate Easily. Slovakia Correct??

Kc

 

80,000 km. No DTCs. New tires. Leak-free exhaust. Hiss does not change with engine speed. It also does this at idle when the car is in motion.

 

Any Mods To Car At All or Completely Stock??

You Got My Noodle in Research Mode! Usually I Latch On To an Issue and Wake Up In The Middle of The Night and it Comes To Me!

KC

 

I would also like to know if this car is OEM stock or if you've done any mods, particularly to the suspension as in airbag suspension...

 

The car is complete OEM 😁

 

Any check engine lights or anything? Perhaps the hissing noises may sound like they're coming from the rear, but could actually be coming from the front... it's also possible it may also be coming from the EVAP cannister or perhaps even a breather filter device located in the fuel tank...Otherwise, I'm completely stumped

 

The sound is definitely coming from the back. Up to about 20 mph the sound is not heard at all.

 

Then in that case, I'm completely stumped! Therefore, I would suggest talking your car to a reliable service center and explain the hissing issues along with all the troubleshooting steps you've taken...

Perhaps they can figure out, diagnose and locate where the hissing noises are coming from...

 

Is it only there when the car is in motion?

You mentioned new tires... What brand did you put on? Could it be the tires making the noise?

 

Yes, only in motion. It's best to hear it when I drive about 40 and then put it in neutral and let off the gas. It's definitely not tires. I think it's either the drive shaft or the differential.