I am hearing a sound when I start the car and when it drives over hills. I hear a hissing sound. It rides fine, but seems like the struts may be bad or going what. Any recommendations?
It sounds that there might be a leak in a strut or a line going towards it. The links under airmatic at https://www.benzworld.org/forums/w221-s-class/2340705-diy-faq-chassis-brakes-exhaust-steering.html may be helpful to you.
Your suspension should be hydraulic (oil filled) and there should not be any hissing sounds like you hear with the air suspension.
Do you hear the sounds when stopped with the engine running?