Hissing under passenger side dash???

[Grinchvr6]

I currently have a 2002 Explorer (4.0L) I have had it for about 6 months, and just yesterday I noticed a hissing sound under the dash on the passenger side when I accelerate lightly. I also hear it when I shut the car off. It only hisses for a few seconds during these situations. I looked under the dash and noticed colored vacuum lines...I checked them over and they appear to be attatched and in good shape. It appears that there are spots for about 7 lines, but only 6 are used..the top one was left alone. Are the sounds Im hearing normal?..is there a release valve thats making this noise?..or do I have a leak? Sorry to be long winded, I just wanted to include as much info as possible. thank you!

 

[drivehard]

dont worry its just the neighbors 12 ft long python

 

[Interstate]

I was told it was the AC, (by some guy, so I can't use him as verification) But I hear that sort of thing too. ('02 sport 4.0) I begging to think it is the AC because when I shut the engine off and get out, I can hear it by the right front wheel.