Did you ever resolve your issue. I am new to this forum and reading older posts. I have an 08 Endeavor. The last couple of months I too get a little hissing of air after shut down. Often just a bit more hissing when I step out. As if it is leveling back up due to my wieght. I'm not heavy at 180 lbs. I haven't tried real hard to find it. I did set my ride height a couple of weeks ago so that helped me get familiar with the setup. The hissing was there before touching anything. It might be a normal thing and mine is just now working correctly. They threw these last coaches together and I have found many poor workmanship items. The ride height was 1.5 inches low in the front. The additional pressure to bring it up really improved the handling.