Hey Ed, I saw your post. I have an 05 Journey. They have Neway suspensions usign Firestone Airsprings. I was a development engineer at Firestone in Noblesville Indiana (they are no longer made there, I believe they moved to TN). Anyway, you have Neways 1T15K1's on the frone and 1T15K2's on the rear. These airsprings have an aluminum pistons on the bottom and the tops are crimped plates. They are a rolling T style. A better ride than bellows type. I suspect the hissing sound you heard came from the leveling valve. They have a three second delay. So when you go over the bumb or pothole they do not give a knee jerk reaction. They use a silicone fluid to slow down the action. If you load or unload the coach with significant weight they will adjust the ride height. I work with Tom Carpenter in Noblesville, he did all the initial Ride Rite designs. I worked on the molds for those units. Every airspring was leak check using 8% nitrous oxide in a cabinet with a sniffer that detected leaks. Those airsprings are very durable even though the cord is only .035" diameter. I know I'm a little late but if you need info on this suspension, just contact me. I know all about them. I went to Gaffney last year to see Freightliner build the chassis- worth the trip.