2001 BMW X5 haveing problems with my back air suspension on

Hello, my name is fridys. 1 week ago I was going to work. Wen I wentt drive my 2001 x5, I saw the back of my x5 lower then the front. So I open the door to drive, and heard a noise of kind of like a small moter hamiing noise, fo a few secounds. When i
turn on the x5 the noise stop. Also it went back to normal, back up from the back. What can you tell me
about this problem or what part should I buy. Please help me. Thank you fridys leyba
my phone # 305-631-0013