My seville is riding awfully low in the back when no one is even sitting in the back and when someone sits in the back the car almost hits theground and i cant seem to figure out why! My mechanic said it may be the air ride or something. Any suggestions?

Probably the air ride. Have the air lines and connections checked for damage and see if the air compressor still works. The air bags could be bad also. You will just have to pump the system up and listen carefully. You may want to have a spray bottle with soapy water too so if you think something is leaking spray it and see if it makes bubbles.